Effects of omega-3 fatty acids on intravascular lipolysis of very-low-density lipoproteins in humans

Omega 3 Improves Both apoB100-containing Lipoprotein Turnover and their Sphingolipid Profile in Hypertriglyceridemia

CONTEXT

Evidence for an association between sphingolipids and metabolic disorders is increasingly reported. Omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) improve apolipoprotein B100 (apoB100)-containing lipoprotein metabolism, but their effects on the sphingolipid content in lipoproteins remain unknown.

OBJECTIVES

In subjects with hypertriglyceridemia, we analyzed the effect of n-3 LC-PUFAs on the turnover apoB100-containing lipoproteins and on their sphingolipid content and looked for the possible association between these lipid levels and apoB100-containing lipoprotein turnover parameters.

METHODS

Six subjects underwent a kinetic study before and after n-3 supplementation for 2 months with 1 g of fish oil 3 times day containing 360 mg of eicosapentaenoic acid (EPA) and 240 mg of docosahexaenoic acid (DHA) in the form of triglycerides. We examined apoB100-containing lipoprotein turnover by primed perfusion labeled [5,5,5-2H3]-leucine and determined kinetic parameters using a multicompartmental model. We quantified sphingolipid species content in lipoproteins using mass spectrometry.

RESULTS

Supplementation decreased very low-density lipoprotein (VLDL), triglyceride, and apoB100 concentrations. The VLDL neutral and polar lipids showed increased n-3 LC-PUFA and decreased n-6 LC-PUFA content. The conversion rate of VLDL1 to VLDL2 and of VLDL2 to LDL was increased. We measured a decrease in total apoB100 production and VLDL1 production. Supplementation reduced the total ceramide concentration in VLDL while the sphingomyelin content in LDL was increased. We found positive correlations between plasma palmitic acid and VLDL ceramide and between VLDL triglyceride and VLDL ceramide, and inverse correlations between VLDL n-3 LC-PUFA and VLDL production.

CONCLUSION

Based on these results, we hypothesize that the improvement in apoB100 metabolism during n-3 LC-PUFA supplementation is contributed to by changes in sphingolipids.

Influence of feeding a fish oil-containing diet to mature, overweight dogs: Effects on lipid metabolites, postprandial glycaemia and body weight

The objective of this study was to determine the effect of feeding a fish oil (FO)-containing diet on lipid and protein metabolism, postprandial glycaemia and body weight (BW) of mature, overweight dogs. Seven female dogs were randomly assigned to one of two isonitrogenous and isocaloric diets, control (CO) or FO (FO), in a crossover design. Experimental periods were 69 day, separated by a washout period of 30 day. At the beginning of the experiment, and at 30 and 60 day of feeding the experimental diets, the dogs were infused with D-glucose (2 g/kg BW) through an intravenous catheter. Blood samples were collected for 3 hr to perform a glucose tolerance test. Nitrogen balance measurements began at 06:30 on d 63 of each experimental period and ended at 06:30 on d 69. On d 66 of each period, a single dose (7.5 mg/kg) of ¹⁵ N-glycine was administered orally for determination of protein turnover. Incremental area under the curve and glucose concentration at peak did not differ between treatments or among sampling days within treatment. Glucose half-life tended to decrease (p < .10) in the FO treatment on day 30 when compared to baseline (day 0). β-hydroxybutyrate, non-esterified fatty acid (NEFA) and triglycerides did not differ within or between treatments. Cholesterol decreased (p < .05) on the FO treatment on day 30, 60 and 69 when compared to day 0. High-density lipoprotein (HDL) decreased (p < .05) in the FO treatment on day 69 when compared to day 0. Body weight, food intake, faecal excretion, DM and N digestibilities, N balance and protein turnover were not different between diets. Overall, FO-containing diet decreases cholesterol in mature overweight dogs; however, further research is warranted to verify the effects of FO on glucose metabolism.

Influence of feeding a fish oil-containing diet to young, lean, adult dogs: effects on lipid metabolites, postprandial glycaemia and body weight

The aim of this study was to determine the effect of feeding a fish oil (FO)-containing diet on lipid and protein metabolism, postprandial glycaemia and body weight in young, lean, adult dogs. Eight female Beagles were randomly assigned to one of two isonitrogenous and isoenergetic diets, Control or FO, in a crossover design. At the beginning of the experiment and at 30 and 60 d, a baseline blood sample was collected and the dogs then were fed their daily ration. Nitrogen balance began at 07:00 h on day 63 of each experimental period and ended at 07:00 h on day 69. On day 66 of each period, a single dose (7.5 mg/kg) of (15)N-glycine was administered orally to each dog via gelatin capsule. Postprandial glycaemia did not differ between treatments or among sampling days within treatment. Cholesterol concentration was increased (p<0.05) on the Control treatment throughout the experiment when compared to values of day 0. Dogs fed the FO treatment had higher plasma triglyceride and ghrelin concentrations than those fed the Control treatment. Body weight and food intake did not differ between dietary treatments. Faecal excretion was increased (p<0.05) in the FO treatment. Dry matter digestibility was decreased (p<0.05) and fat digestibility tended (p<0.10) to decrease in the FO treatment. Overall, feeding a FO-containing diet showed a protective effect against the rise of plasma cholesterol and it increased plasma ghrelin concentration. However, FO supplementation did not appear to affect protein metabolism or postprandial glycaemia in adult lean dogs.

Effect of Omega-3 fatty acids on blood pressure and serum lipids in continuous ambulatory peritoneal dialysis patients

OBJECTIVE

Hypertension and hyperlipidemia are two major risk factors for cardiovascular disease in continuous ambulatory peritoneal dialysis (CAPD) patients. This study was designed to investigate the effect of omega-3 fatty acids on blood pressure (BP) and serum lipids in CAPD patients.

METHODS

This study was a randomized double-blind clinical trial in which 90 CAPD patients were randomly assigned to either the omega-3 or the placebo group. Patients in omega-3 group received 3 g/day omega-3 for 8 weeks, whereas patients in the control group received placebo. At baseline and at the end of 8 weeks, the patients' BP was controlled, and serum biochemistry was measured.

FINDINGS

Mean systolic BP decreased (-22.2 ± 14.2 mmHg) in the omega-3 group at the end of the study while in the placebo group increased (+0.5 ± 30.2 mmHg) (P < 0.0001). Mean diastolic BP of the omega-3 group decreased more (-11.95 ± 11.9 mmHg) comparing with the placebo group (-1.1 ± 17.3 mmHg) (P = 0.001). There were no significant differences between the two groups in mean changes in serum triglyceride, and total, high-density lipoprotein, and low-density lipoprotein cholesterol.

CONCLUSION

The results of this study indicate that omega-3 reduced BP significantly but had no effect on lipid profile in our CAPD patients.

Effects of increases in dietary fat intake on plasma lipid and lipoprotein cholesterol concentrations and associated enzyme activities in cats

OBJECTIVE

To determine the effects of increases in dietary intake of polyunsaturated and saturated fatty acids on plasma lipid and lipoprotein concentrations and activity of associated enzymes in healthy domestic cats.

ANIMALS

16 healthy adult sexually intact female cats.

PROCEDURES

A baseline diet (40% energy from fat) and 4 test diets, with increased amounts of fat (51% and 66% energy from fat) from the addition of polyunsaturated and saturated fatty acids, were fed for 6 weeks each. Plasma cholesterol, triglyceride, and lipoprotein cholesterol concentrations, along with activities of lipoprotein lipase, hepatic lipase, and lecithin-cholesterol acyl transferase, were measured at the end of each feeding period.

RESULTS

Diet, amount of fat, or ratio of polyunsaturated to saturated fatty acids had no effect on plasma concentrations of cholesterol, triglycerides, and very-low-density or high-density lipoproteins or the activity of lecithin-cholesterol acyl transferase. Low-density lipoprotein concentrations were significantly lower in cats fed a high-fat diet containing polyunsaturated fatty acids. Lipoprotein concentration and hepatic lipase activity were significantly higher in cats fed the fat-supplemented diets, and this was unrelated to whether diets were enriched with polyunsaturated or saturated fatty acids.

CONCLUSIONS AND CLINICAL RELEVANCE

Diets containing up to 66% of energy from fat were tolerated well by healthy cats and did not affect plasma lipid concentrations. Therefore, high-fat diets probably will not contribute to hypercholesterolemia or hypertriglyceridemia in cats.

PPARalpha L162V polymorphism alters the potential of n-3 fatty acids to increase lipoprotein lipase activity

Omega-3 fatty acids (FAs) may accelerate plasma triglyceride (TG) clearance by altering lipoprotein lipase (LPL) activity. Yet, the ability of n-3 FAs to increase LPL activity is dependent on transcription factors such as peroxisome proliferator-activated receptor alpha (PPARalpha). The objective was to examine the effects of n-3 FAs on LPL activity considering the occurrence of PPARalpha L162V polymorphism. First, 14 pairs of men either L162 homozygotes or carriers of the V162 allele were supplemented with n-3 FAs. Second, transient transfections in HepG2 cells, for the L162- and V162-PPARalpha variants with the peroxisome proliferator-response element from the human LPL gene, were transactivated with n-3 FAs. In vivo results demonstrate that the LPL activity increased non-significantly by 14.4% in L162 homozygotes compared with 6.6% in carriers of the PPARalpha-V162 allele, after n-3 FA supplementation. Additionally, the L162 homozygotes tended towards an inverse correlation between LPL activities and plasma TG levels. Conversely, carriers of the V162 allele showed no such relationship. In vitro data demonstrates that transcription rates of LPL tended to be higher for the L162-PPARalpha than V162-PPARalpha after n-3 FAs activation. Overall, these results indicate that n-3 FA supplementation increases the transcription rate of LPL to a greater extent in L162-PPARalpha than V162-PPARalpha.

Echium oil reduces plasma lipids and hepatic lipogenic gene expression in apoB100-only LDL receptor knockout mice

We tested the hypothesis that dietary supplementation with echium oil (EO), which is enriched in stearidonic acid (SDA; 18:4 n-3), the product of Delta-6 desaturation of 18:3 n-3, will decrease plasma triglyceride (TG) concentrations and result in conversion of SDA to eicosapentaenoic acid (EPA) in the liver. Mildly hypertriglyceridemic mice (apoB100-only LDLrKO) were fed a basal diet containing 10% calories as palm oil (PO) and 0.2% cholesterol for 4 weeks, after which they were randomly assigned to experimental diets consisting of the basal diet plus supplementation of 10% of calories as PO, EO or fish oil (FO) for 8 weeks. The EO and FO experimental diets decreased plasma TG and VLDL lipid concentration, and hepatic TG content compared to PO, and there was a significant correlation between hepatic TG content and plasma TG concentration among diet groups. EO fed mice had plasma and liver lipid EPA enrichment that was greater than PO-fed mice but less than FO-fed mice. Down-regulation of several genes involved in hepatic TG biosynthesis was similar for mice fed EO and FO and significantly lower compared to those fed PO. In conclusion, EO may provide a botanical alternative to FO for reduction of plasma TG concentrations.

Effect of n-3 fatty acids on metabolism of apoB100-containing lipoprotein in type 2 diabetic subjects

The effect of long-chain n-3 PUFA on the metabolism of apoB100-containing lipoprotein in diabetic subjects is not fully understood. The objective of the present study was to determine the effect of a daily intake of 1080 mg EPA and 720 mg DHA for diabetic subjects on the kinetics of apoB100-containing lipoprotein in the fasting state. A kinetic study was undertaken to determine the mechanisms involved in the effects of n-3 fatty acids in terms of a decrease in triacylglycerol level in type 2 diabetic patients. We have studied the effect of fish oils on the metabolism of apoB100 endogenously labelled by [5,5,5-2H3]-leucine in type 2 diabetic patients in the fasting state. The kinetic parameters of apoB100 in VLDL, intermediate-density lipoprotein and LDL were determined by compartmental modelling in five diabetic subjects before and 8 weeks after n-3 fatty acid treatment. Treatment did not change the plasma cholesterol level (0.801 (sd 0.120) v. 0.793 (sd 0.163) mmol/l) but lowered the plasma triacylglycerol level (1.776 (sd 0.280) v.1.356 (sd 0.595) mmol/l; P < 0.05). Treated patients showed a decrease in VLDL apoB100 concentration (0.366 (sd 0.030) v.0.174 (sd 0.036) g/l; P < 0.05) related to a decrease in VLDL 1 production (1.49 (sd 0.23) v.0.44 (sd 0.19) mg/kg per h; P < 0.05) and an increase in the VLDL conversion rate (0.031 (sd 0.024) v.0.052 (sd 0.040) per h; P < 0.05), with no change in fractional catabolic rates. Treatment led to a higher direct production of intermediate-density lipoprotein (0.02 (sd 0.01) v.0.24 (sd 0.12) mg/kg per h; P < 0.05). In conclusion, the present study, conducted in the fasting state, showed that supplementation with n-3 fatty acids in type 2 diabetic patients induced beneficial changes in the metabolism of apoB100-containing lipoprotein.

Use of a fish oil-based lipid emulsion to treat essential fatty acid deficiency in a soy allergic patient receiving parenteral nutrition

The treatment of essential fatty acid deficiency (EFAD) in a 17-year-old male following allogeneic bone marrow transplantation is described. His transplant was complicated by gastrointestinal bleeding that precluded the use of enteral feedings. Due to a severe soy allergy, he could not tolerate any intravenous fat emulsions marketed in the US. After months of receiving fat-free parenteral nutrition and intermittent use of enteral feeds, he developed signs and symptoms consistent with EFAD, including a rash and an elevated plasma triene:tetraene ratio of 0.231 (0.013-0.05). After receiving FDA approval, a parenteral fish oil emulsion was administered to provide fat calories and sufficient alpha-linolenic and linoleic acid to correct his EFAD. Therapy was initiated at 0.2 g/kg/day and advanced to 0.67 g/kg/day, providing approximately 45 mg/kg/day of linoleic acid. After 10 days of therapy, his rash disappeared and his triene:tetraene ratio improved to 0.07. By day 17 the ratio normalized to 0.047. This suggests that using a fish oil emulsion with minimal linoleic acid may be safely used as the sole source of fat calories and may be an option to prevent or treat EFAD in subjects allergic to soy that require a parenteral source of fat.

Mechanisms by which dietary fatty acids modulate plasma lipids

Dietary fatty acids have a considerable effect on plasma LDL cholesterol (LDL-C) concentrations and therefore on the risk for coronary heart disease. Numerous studies have been conducted in animal models to elucidate the mechanisms by which different types of fatty acids modulate plasma cholesterol concentrations. In addition, multiple clinical trials and epidemiological data have demonstrated the effects of fatty acids in determining the concentrations of circulating LDL. SFAs and trans fatty acids have a detrimental effect on plasma lipids, whereas PUFAs of the (n-6) family and monounsaturated fatty acids decrease plasma LDL-C concentrations. Among the SFAs, stearic acid (18:0) appears to have a neutral effect on LDL-C, while lauric (12:0), myristic (14:0), and palmitic (16:0) acids are considered to be hypercholesterolemic. SFAs increase plasma LDL-C by increasing the formation of LDL in the plasma compartment and by decreasing LDL turnover. Although unsaturated fatty acids increase cholesterol synthesis, they also increase hepatic LDL receptor number and LDL turnover in vivo. Fatty acids are also ligands of important regulatory elements, which can play a role in determining plasma cholesterol. This article presents a summary of the major effects of various types of fatty acids on plasma lipid concentrations and the mechanisms involved.

Omega-3 fatty acids alter lipoprotein subfraction distributions and the in vitro conversion of very low density lipoproteins to low density lipoproteins

The purpose of this study was to determine the effects of a fish oil concentrate (FOC) on the in vitro conversion of very low density lipoproteins (VLDL) to intermediate (IDL) and low density lipoproteins (LDL). Six hypertriglyceridemic patients were randomly allocated to receive either placebo (olive oil) or FOC (1 g/14 kg body weight/day) for 4 weeks in a crossover study with a 4-week washout period. The FOC provided 3 g of eicosapentaenoic + docosahexaenoic acid per 70 kg of body weight, and it lowered plasma triglyceride and VLDL cholesterol levels by 35% and 42%, respectively. Decreases in the largest particles (VLDL(1)) were primarily responsible, with no effect noted in smaller VLDL particles (VLDL(2) and VLDL(3)). The FOC increased LDL cholesterol levels by 25% (P < 0.06) but did not affect LDL particle size. VLDL(1) and VLDL(3) were incubated in vitro with human postheparin lipases. Although triglycerides from both types of VLDL were hydrolyzed to the same extent with both treatments, particles isolated during the FOC phase were more readily converted into IDL and LDL than were control particles. These data suggest that the marine omega3 fatty acids may enhance the propensity of VLDL to be converted to LDL, partly explaining the decreased VLDL and increased LDL levels in FOC-treated patients.

Effects of walnut consumption on plasma fatty acids and lipoproteins in combined hyperlipidemia

BACKGROUND

Epidemiologic studies show an inverse relation between nut consumption and coronary heart disease.

OBJECTIVE

We determined the effects of walnut intake on plasma fatty acids, lipoproteins, and lipoprotein subclasses in patients with combined hyperlipidemia.

DESIGN

Participants sequentially adhered to the following diets: 1) a habitual diet (HD), 2) a habitual diet plus walnuts (HD+W), 3) a low-fat diet (LFD), and 4) a low-fat diet plus walnuts (LFD+W).

RESULTS

In 13 postmenopausal women and 5 men ( +/- SD age 60 +/- 8 y), walnut supplementation did not increase body weight despite increased energy intake and the LFD caused weight loss (1.3 +/- 0.5 kg; P < 0.01). When comparing the HD with the HD+W, linoleic acid concentrations increased from 29.94 +/- 1.14% to 36.85 +/- 1.13% and alpha-linolenic acid concentrations increased from 0.78 +/- 0.04% to 1.56 +/- 0.11%. During the LFD+W, plasma total cholesterol concentrations decreased by 0.58 +/- 0.16 mmol/L when compared with the HD and by 0.46 +/- 0.14 mmol/L when compared with the LFD. LDL-cholesterol concentrations decreased by 0.46 +/- 0.15 mmol/L when compared with the LFD. Measurements of lipoprotein subclasses and particle size suggested that walnut supplementation lowered cholesterol preferentially in small LDL (46.1 +/- 1.9% compared with 33.4 +/- 4.3%, HD compared with HD+W, respectively; P < 0.01). HDL-cholesterol concentrations decreased from 1.27 +/- 0.07 mmol/L during the HD to 1.14 +/- 0.07 mmol/L during the HD+W and to 1.11 +/- 0.08 mmol/L during the LFD. The decrease was seen primarily in the large HDL particles.

CONCLUSIONS

Walnut supplementation may beneficially alter lipid distribution among various lipoprotein subclasses even when total plasma lipids do not change. This may be an additional mechanism underlying the antiatherogenic properties of nut intake.

Reduced hepatic triglyceride secretion in rats fed docosahexaenoic acid-rich fish oil suppresses postprandial hypertriglyceridemia

To evaluate the mechanisms of suppression of postprandial hypertriglyceridemia by fish oil rich in docosahexaenoic acid, the effect on the intestinal absorption of triglyceride, activities of lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) and metabolism of chylomicrons (CM) and CM remnants were compared with that of safflower oil in Sprague-Dawley rats in a series of studies. The feeding of fish oil for 3 wk suppressed postprandial hypertriglyceridemia (study 1). Dietary fish oil did not alter the rate of lymphatic absorption of triglyceride (study 2). The activities of LPL and HTGL were measured at 5 h after the beginning of feeding, when serum triglyceride concentrations were highest in both dietary groups. The activities of LPL in adipose tissue and heart were greater (P < 0.05) and those of HTGL were lower (P < 0.05) in the rats fed fish oil (study 3). In contrast, there were no differences in the activities of LPL and HTGL in postheparin plasma between the fish and safflower oil groups (study 4). The clearance rates of CM and CM remnants were measured by injecting intravenously CM collected from rats fed safflower or fish oils with [14C]triolein and [3H]cholesterol (study 5). Dietary oil did not influence the half-lives of CM or CM remnants. The secretion of triglyceride from the liver of rats injected with Triton WR-1339 was lower (P < 0.05) in the rats fed docosahexaenoic acid, a major component of fish oil, than those fed linoleic acid, a major component of safflower oil (study 6). These observations strongly support the hypothesis that in rats, the principal cause of the suppression of postprandial hypertriglyceridemia by fish oil is the depression of triglyceride secretion from the liver.

Changes in plasma lipoproteins during low-fat, high-carbohydrate diets: effects of energy intake

BACKGROUND

Low-fat diets can increase plasma triacylglycerol and reduce HDL cholesterol. Changes in energy intake and body weight can influence the lipoprotein response.

OBJECTIVE

We sought to prospectively examine the effects of euenergetic and ad libitum dietary fat restriction on plasma lipoproteins in healthy postmenopausal women.

DESIGN

Participants first received a controlled euenergetic diet in which dietary fat was reduced stepwise from 35% to 25% to 15% over 4 mo. Thereafter, participants followed an ad libitum 15%-fat diet for 8 mo; 54 women completed the intervention.

RESULTS

During the controlled euenergetic diet, plasma triacylglycerol increased from 1.70 +/- 0.10 to 2.30 +/- 0.16 mmol/L, total cholesterol decreased from 5.87 +/- 0.13 to 5.53 +/- 0. 13 mmol/L, LDL cholesterol decreased from 3.41 +/- 0.10 to 2.87 +/- 0.10 mmol/L, HDL cholesterol decreased from 1.76 +/- 0.08 to 1.50 +/- 0.08 mmol/L, and apolipoprotein (apo) A-I decreased from 5.11 +/- 0.14 to 4.78 +/- 0.14 mmol/L (P < 0.0001 for all changes). Hormone replacement therapy did not affect the relative change in HDL cholesterol. Plasma glucose, insulin, hemoglobin A(1C,) free fatty acid, and apo B concentrations did not change significantly. During the ad libitum 15%-fat diet, participants lost 4.6 +/- 0.4 kg. Plasma triacylglycerol and LDL cholesterol returned to baseline values (1.77 +/- 0.12 and 3.31 +/- 0.08 mmol/L, respectively), whereas HDL cholesterol and apo A-I remained low (1.40 +/- 0.08 and 4.82 +/- 0.18 mmol/L, respectively). HDL cholesterol and apo A-I concentrations stabilized in subjects who were not receiving hormone replacement therapy but continued to decline in women who were receiving hormone therapy.

CONCLUSIONS

The ad libitum 15%-fat diet resulted in significant weight loss. The euenergetic but not the ad libitum diet caused hypertriacylglycerolemia. HDL cholesterol decreased during both low-fat diets.

Long-chain n-3 polyunsaturated fatty acids and triacylglycerol metabolism in the postprandial state

Elevated plasma triacylglycerol (TG; triglyceride) concentrations, especially in the postprandial state, have been associated with an increased risk of coronary heart disease (CHD). Postprandial lipemia represents a complex series of reactions which occur following the ingestion of a meal containing fat and is associated with a number of adverse metabolic events including the production of atherogenic chylomicron remnants, the formation of the highly atherogenic small dense low density lipoprotein particles, a reduction in the concentration of the cardioprotective high density lipoprotein fraction and the activation of coagulation factor VII. Fish oils are a rich source of the long-chain n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid and docosahexaenoic acid. Long chain n-3 PUFA are effective hypotriglyceridemic agents, lowering both fasting and postprandial TG concentrations. There is a large body of evidence which shows that n-3 PUFA reduces plasma TG concentrations through reduced endogenous very low density lipoprotein production. This in turn may account for the reduced postprandial lipemic response following n-3 PUFA supplementation. However, this does not preclude a contribution of enhanced chylomicron clearance, which may be mediated through altered chylomicron size, structure or chemical composition, or altered lipoprotein lipase metabolism in terms of enzyme concentration, activity, or affinity for chylomicrons. However the precise biochemical nature of this effect remains to be established. The reduction of postprandial plasma TG concentrations by n-3 PUFA may partly explain why n-3 PUFA intake is inversely related to CHD mortality.

The mechanism underlying the hypocholesterolemic effect of chronic fish oil feeding in rats is not due to increased excretion of dietary cholesterol

The role of the excretion of dietary cholesterol in the hypocholesterolaemic effect of chronic fish oil feeding in rats was investigated. The hepatic uptake and processing of [3H]cholesterol carried in chylomicrons derived from fish oil was studied in vivo in rats fed a low fat diet or a diet supplemented with fish oil for 21 days. In addition, the effects of the fish oil diet on cholesterol esterification, cholesteryl ester hydrolysis, bile acid synthesis and biliary lipid secretion were determined. In rats fed the fish oil as compared to the low fat diet, the uptake of [3H]cholesterol from the blood and its secretion into bile as bile acids was significantly slower, and this was entirely due to a decrease in the bile acid fraction. Biliary bile acid mass secretion was unchanged by fish oil feeding, while biliary cholesterol and phospholipid secretion was increased. No significant differences were observed either in the expression of mRNA for cholesterol 7alpha hydroxylase or the secretion of bile acids into bile after 20 h biliary drainage between the fish oil and low fat diet groups, suggesting that bile acid synthesis is not affected. These results indicate that the access of chylomicron cholesterol to the hepatic substrate pool for bile acid formation is decreased in the fish oil fed rats, and this, together with its slower uptake from the blood, accounts for the retardation of its excretion via the bile. Thus, the hypocholesterolemic effect of dietary fish oil in rats is not due to more rapid metabolism of cholesterol originating from the diet.

Effects of Simvastatin and omega-3 fatty acids on plasma lipoproteins and lipid peroxidation in patients with combined hyperlipidaemia

OBJECTIVES

Patients with combined hyperlipidemia are at increased risk for development of coronary heart disease. The purpose of this study was to evaluate the efficiency and the safety of treatment with Simvastatin and omega-3 fatty acids in patients with this lipid disorder.

DESIGN

A double-blind placebo controlled, randomized study evaluating the effects of Simvastatin separately and in combination with omega-3 fatty acids in 41 healthy patients with defined hyperlipidemia. After a 16 weeks dietary run-in period the patients were treated in periods of 5 weeks.

RESULTS

As expected Simvastatin (20 mg day[-1]) reduced serum total cholesterol, triacylglycerols, apolipoproteins B and E and increased HDL-cholesterol and apolipoprotein A1. Addition of omega-3 fatty acids (4 g day[-1]) further decreased serum triacylglycerols (P = 0.007), total cholesterol (P = 0.052) and apolipoprotein E (P = 0.035). No significant changes attributable to supplementation of polyunsaturated fatty acids on the content of lipid peroxides in plasma and in the various lipoprotein fractions were observed.

CONCLUSIONS

The combined treatment of Simvastatin and omega-3 fatty acids seems to be an efficient and safe alternative for patients with combined hyperlipidemia.

Effects of dietary fat restriction on particle size of plasma lipoproteins in postmenopausal women

Hypertriglyceridemia is an independent risk factor for coronary artery disease (CAD) and is also commonly associated with other coronary risk factors, ie, small, dense low-density lipoprotein (LDL) particles and low plasma levels of high-density lipoprotein cholesterol (HDL-C). Dietary fat restriction is recommended for the prevention of nutrition-related cancers. Low-fat, high-carbohydrate intake can increase plasma triglyceride (TG) and decrease HDL-C. In general, plasma TG levels are inversely related to the particle size of LDL. We investigated the effects of dietary fat restriction on the concentration and particle size of plasma lipoproteins in 14 healthy postmenopausal women (aged 61 +/- 11 years). During a 4-month period of eucaloric controlled feeding, dietary fat was reduced stepwise from a habitual intake of 33% +/- 8% to 23% and then to 14% of daily energy. Changes in the plasma lipid level and particle size of very-low-density lipoprotein (VLDL), LDL, and HDL were determined at the end of each dietary phase. Increasing carbohydrate intake without weight loss was associated with an increase in plasma TG (1.86 +/- 0.30 v 2.47 +/- 0.37 mmol/L) and decreases in total cholesterol (5.82 +/- 0.25 v 5.40 +/- 0.21 mmol/L), LDL-C (3.07 +/- 0.18 v 2.61 +/- 0.21 mmol/L), HDL-C (1.42 +/- 0.1 v 1.24 +/- 0.1 mmol/L), and apolipoprotein (apo) A1 (5.14 +/- 0.25 v 4.61 +/- 0.36 mmol/L), whereas plasma apo B did not change. The particle size of VLDL increased (42.7 +/- 1.4 v 47.0 +/- 0.9 nm). However, there was no change in either LDL (25.1 +/- 0.2 v 25.3 +/- 0.2 nm) or HDL particle size. Although at each level of dietary fat intake LDL particle size correlated inversely with plasma TG and apo B, there was no relationship between the increase in plasma TG and LDL particle size. These results show that hypertriglyceridemia caused by a eucaloric high-carbohydrate intake is not associated with a decrease in LDL particle size. Therefore, carbohydrate-induced hypertriglyceridemia may not have the same atherogenic potential as genetic hypertriglyceridemias.

Effects of n-3 fatty acids and fenofibrate on lipid and hemorrheological parameters in familial dysbetalipoproteinemia and familial hypertriglyceridemia

There is increasing evidence that hemorrheological abnormalities are associated with an enhanced risk of atherosclerosis. The n-3 fatty acids (n-3-FA) have been shown to have beneficial effects on atherosclerosis in patients with dyslipoproteinemias. We studied 23 patients with elevated plasma triglycerides to evaluate the influence of fish oil and fenofibrate therapy on hemorrheological parameters (15 patients with familial hypertriglyceridemia [FHTG] and eight with familial dysbetalipoproteinemia [FDL]). The patients (one woman and 22 men aged 45.7 +/- 2.0 years) were treated with increasing doses of n-3-FA (1.8 to 3.6 g/d: 0.9 to 1.8 g eicosapentaenoic acid and 0.6 to 1.2 g docosahexaenoic acid) for 8 weeks. Lipid parameters, whole-blood viscosity at different shear rates, plasma viscosity, fibrinogen concentration, and red blood cell aggregation (RCA) were measured at baseline and at weeks 2, 4, 8 (end of n-3-FA therapy), and 12. Compliance was ensured by measuring plasma concentrations of eicosapentaenoic acid and docosahexaenoic acid. After 12 weeks, patients began treatment with fenofibrate (250 mg daily); investigations were performed again at week 20. Total triglycerides (from 6.90 +/- 1.70 to 3.61 +/- 0.78 mmol/L in FDL and 7.44 +/- 1.50 to 4.15 +/- 0.55 in FHTG), very-low-density lipoprotein (VLDL) triglycerides, and VLDL cholesterol were significantly decreased with n-3-FA therapy in both groups (P < .05). In FHTG, low-density lipoprotein (LDL) cholesterol increased significantly (from 2.75 +/- 0.28 to 3.97 +/- 0.35 mmol/L, P < .01); in FDL, total cholesterol decreased (from 9.76 +/- 1.32 to 7.34 +/- 1.07 mmol/L, P < .05). No significant changes were observed in hemorrheological parameters, except for reduced RCA with 3.6 g n-3-FA in FHTG. However, with fenofibrate therapy, in addition to comparable lipoprotein changes seen with fish oil, fibrinogen levels and plasma and blood viscosity decreased in patients with FDL. We conclude that n-3-FA and fenofibrate have comparable effects on lipid parameters in patients with FDL and FHTG. Because of additional beneficial effects on hemorrheological parameters, fenofibrate may be preferred for the treatment of FDL.