Docosahexaenoic acid shows no triglyceride-lowering effects but increases the peroxisomal fatty acid oxidation in liver of rats

Differential effects of long chain n-3 fatty acids on the expression of PGH synthase isoforms in bovine aortic endothelial cells

Primary cultures of bovine aortic endothelial cells were used at confluency to evaluate the effect of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids on the expression of both the constitutive and inducible isoforms of PGH synthase (PGHS), PGHS-1 and PGHS-2, respectively. After a 22 h period enrichment of cell lipid stores with each fatty acid, the expression of PGH synthase isoforms was measured by western blotting. EPA and DHA, but not oleate, significantly decreased the immunoreactive PGHS-1 and to a similar extent the corresponding mRNA, as measured by northern blotting. Studies on mRNA stability failed to show any difference between DHA-enriched and control cells, indicating that the decreased expression observed was likely from transcriptional origin. Under the enrichment conditions, EPA and DHA, but not oleate, moderately but significantly induced an oxidative stress as judged by malondialdehyde formation. Interestingly, hydrogen peroxide was able to mimic the effect of EPA and DHA in decreasing the expression of PGHS-1. On the other hand, the PMA-induced PGHS-2 expression could be potentiated by cell pre-enrichment with DHA, whereas hydrogen peroxide alone could induce such an expression. We conclude that the long chain n-3 fatty acids EPA and DHA may differently affect the expression of PGH synthase isoforms, possibly via an oxidative stress.

3-Thia fatty acid treatment, in contrast to eicosapentaenoic acid and starvation, induces gene expression of carnitine palmitoyltransferase-II in rat liver

The aim of the present study was to investigate the hepatic regulation and beta-oxidation of long-chain fatty acids in peroxisomes and mitochondria, after 3-thia- tetradecylthioacetic acid (C14-S-acetic acid) treatment. When palmitoyl-CoA and palmitoyl-L-carnitine were used as substrates, hepatic formation of acid-soluble products was significantly increased in C14-S-acetic acid treated rats. Administration of C14-S-acetic acid resulted in increased enzyme activity and mRNA levels of hepatic mitochondrial carnitine palmitoyltransferase (CPT)-II. CPT-II activity correlated with both palmitoyl-CoA and palmitoyl-L-carnitine oxidation in rats treated with different chain-length 3-thia fatty acids. CPT-I activity and mRNA levels were, however, marginally affected. The hepatic CPT-II activity was mainly localized in the mitochondrial fraction, whereas the CPT-I activity was enriched in the mitochondrial, peroxisomal, and microsomal fractions. In C14-S-acetic acid-treated rats, the specific activity of peroxisomal and microsomal CPT-I increased, whereas the mitochondrial activity tended to decrease. C14-S-Acetyl-CoA inhibited CPT-I activity in vitro. The sensitivity of CPT-I to malonyl-CoA was unchanged, and the hepatic malonyl-CoA concentration increased after C14-S-acetic acid treatment. The mRNA levels of acetyl-CoA carboxylase increased. In hepatocytes cultured from palmitic acid- and C14-S-acetic acid-treated rats, the CPT-I inhibitor etomoxir inhibited the formation of acid-soluble products 91 and 21%, respectively. In contrast to 3-thia fatty acid treatment, eicosapentaenoic acid treatment and starvation increased the mitochondrial CPT-I activity and reduced its malonyl-CoA sensitivity. Palmitoyl-L-carnitine oxidation and CPT-II activity were, however, unchanged after either EPA treatment or starvation. The results from this study open the possibility that the rate control of mitochondrial beta-oxidation under mitochondrion and peroxisome proliferation is distributed between an enzyme or enzymes of the pathway beyond the CPT-I site after 3-thia fatty acid treatment. It is suggested that fatty acids are partly oxidized in the peroxisomes before entering the mitochondria as acylcarnitines for further oxidation.

Mitochondrial 3-hydroxy-3-methylglutaryl coenzyme A synthase and carnitine palmitoyltransferase II as potential control sites for ketogenesis during mitochondrion and peroxisome proliferation

3-Thia fatty acids are potent hypolipidemic fatty acid derivatives and mitochondrion and peroxisome proliferators. Administration of 3-thia fatty acids to rats was followed by significantly increased levels of plasma ketone bodies, whereas the levels of plasma non-esterified fatty acids decreased. The hepatic mRNA levels of fatty acid binding protein and formation of acid-soluble products, using both palmitoyl-CoA and palmitoyl-L-carnitine as substrates, were increased. Hepatic mitochondrial carnitine palmitoyltransferase (CPT) -II and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase activities, immunodetectable proteins, and mRNA levels increased in parallel. In contrast, the mitochondrial CPT-I mRNA levels were unchanged and CPT-I enzyme activity was slightly reduced in the liver. The CoA ester of the monocarboxylic 3-thia fatty acid, tetradecylthioacetic acid, which accumulates in the liver after administration, inhibited the CPT-I activity in vitro, but not that of CPT-II. Acetoacetyl-CoA thiolase and HMG-CoA lyase activities involved in ketogenesis were increased, whereas the citrate synthase activity was decreased. The present data suggest that 3-thia fatty acids increase both the transport of fatty acids into the mitochondria and the capacity of the beta-oxidation process. Under these conditions, the regulation of ketogenesis may be shifted to step(s) beyond CPT-I. This opens the possibility that mitochondrial HMG-CoA synthase and CPT-II retain some control of ketone body formation.

Effects of docosahexaenoic and eicosapentaenoic acid on lipid metabolism, eicosanoid production, platelet aggregation and atherosclerosis in hypercholesterolemic rats

Exogenously hypercholesterolemic (ExHC) rats were fed on an atherogenic diet supplemented with 1% each of either ethyl ester docosahexaenoic acid [EE-DHA, 22:6(n-3)], ethyl ester eicosapentaenoic acid [EE-EPA, 20:5(n-3)] or safflower oil (SO) for 6 months. The rats fed on the diets containing EE-EPA or EE-DHA, compared with those fed on SO, had lower serum cholesterol and triacylglycerol levels, less aggregation of platelets and slower progress of intimal thickening in the ascending aorta. Relative to the SO-fed rats, both of the (n-3) fatty acid-fed rats had a significantly reduced proportion of arachidonic acid in the platelet and aortic phospholipids, and lower production of thromboxane A2 by platelets and of prostacyclin by the aorta. These results suggest that EPA and DHA are similarly involved in preventing atherosclerosis development by reducing hypercholesterolemia and modifying the platelet functions.

Effects of dietary n-6 and n-3 lipids on antioxidant defense system in livers of exercised rats

OBJECTIVE

The present study was designed to investigate the effects of dietary n-6 and n-3 lipids and exercise on the activities of hepatic antioxidant enzymes and microsomal lipid composition and peroxidation in Fischer-344 male rats.

METHODS

Weanling male Fischer-344 rats were fed ad libitum semipurified diets containing 10% corn oil (CO) or 10% fish oil (FO), with equal levels of antioxidants. After 2 months on the diets, weight-matched animals in each diet group were divided into sedentary (S) and exercised (Ex) groups, and the diets were continued. The animals in the exercise group were run on a treadmill 30 to 40 minutes to exhaustion 6 days/week for 2 months. At the end of 2 months, the rats were sacrificed and livers were collected; antioxidant enzymes were determined in the cytosol, fatty acid composition was analyzed in the microsomes, and vitamin E levels were analyzed in the sera.

RESULTS

The rats in the FO-S group exhibited significantly higher liver cytosolic catalase activity, while their superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were significantly lower compared to the CO-S group. The GSH-Px activity was significantly higher in the FO-Ex group compared to FO-S group. The source of dietary lipids significantly influenced the fatty acid composition of the total lipids in the microsomes. Feeding the FO-based diet significantly increased 18:0 and n-3 fatty acids incorporation into the microsomes (18:3, 20:5, 22:5, and 22:6), whereas ingestion of CO resulted in a significant increase in 14:0, 14:1, 18:1, and n-6 fatty acids (18:2 and 20:4). The serum vitamin E levels were significantly higher in the CO groups, and exercise had no effect on vitamin E levels. Exercise significantly decreased the generation of thiobarbituric acid reactive substances (TBARS) by liver microsomes. Consumption of FO, which is highly susceptible to oxidation, did not show any significant changes in membrane lipid peroxidation.

CONCLUSIONS

The present study suggests that feeding FO increases the activity of liver cytosolic catalase in FO-S rats and GSH-Px in FO-Ex rats. In addition, exercise significantly decreased the generation of TBARS by the liver microsomal lipids. Serum vitamin E levels were higher in the CO group and exercise did not alter vitamin E levels. This suggests that the amount of vitamin E included in the diets was possibly adequate to cope with the oxidative stress induced during exercise.

Low doses of eicosapentaenoic acid, docosahexaenoic acid, and hypolipidemic eicosapentaenoic acid derivatives have no effect on lipid peroxidation in plasma

It was of interest to investigate the influence of both high doses of eicosapentaenoic acid (EPA) and low doses of 2- or 3-methylated EPA on the antioxidant status, as they all cause hypolipidemia, but the dose required is quite different. We fed low doses (250 mg/d/kg body wt) of different EPA derivatives or high doses (1500 mg/d/kg body wt) of EPA and DHA to rats for 5 and 7 d, respectively. The most potent hypolipidemic EPA derivative, 2,2-dimethyl-EPA, did not change the malondialdehyde content in liver or plasma. Plasma vitamin E decreased only after supplementation of those EPA derivatives that caused the greatest increase in the fatty acyl-CoA oxidase activity. Fatty acyl-CoA oxidase activity increased after administration of both EPA and DHA at high doses. High doses of EPA and DHA decreased plasma vitamin E content, whereas only DHA elevated lipid peroxidation. In liver, however, both EPA and DHA increased lipid peroxidation, but the hepatic level of vitamin E was unchanged. The glutathione-requiring enzymes and the glutathione level were unaffected, and no significant changes in the activities of xanthine oxidase and superoxide dismutase were observed in either low- or high-dose experiments. In conclusion, increased peroxisomal beta-oxidation in combination with high amounts of polyunsaturated fatty acids caused elevated lipid peroxidation. At low doses of polyunsaturated fatty acids, lipid peroxidation was unchanged, in spite of increased peroxisomal beta-oxidation, indicating that polyunsaturation is the most important factor for lipid peroxidation.

Variations in dietary fat and cholesterol intakes modify antioxidant status of SHR and WKY rats

The effects of varying dietary fat saturation [butter (B), beef tallow (BT)] or polyunsaturation [(n-6) soybean oil (SBO), (n-3) menhaden oil (MO)] and cholesterol content (0.05 and 0.5 g/100 g) on systolic blood pressure (SBP), plasma lipids and tissue antioxidant status were investigated in 14-wk-old spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. Varying dietary fat composition for 9 wk had no influence on SBP in either SHR or WKY rats. Rats fed MO diets exhibited smaller (P < 0.05) body weight gains, lower (P < 0.05) feed efficiency ratios and lower (P < 0.05) plasma cholesterol concentrations than those fed the B, BT and SBO diets. Significant (P < 0.05) interactions for animal strain x cholesterol intake and animal strain x fat source were noted for serum cholesterol concentrations. SHR exhibited higher (P < 0.05) RBC and liver catalase (CAT), and heart and liver superoxide dismutase (SOD) activities similar to those of WKY rats. The lower (P <0.01) RBC, heart and liver glutathione peroxidase (GSH-Px) activities observed in SHR coincided with higher (P <0.01) glutathione reductase (GSSG-Red), compared with WKY rats. Dietary cholesterol intake had no effect on RBC, heart and liver total sulfhydryl concentration or GSH-Px activities, but increased (P <0. 001) liver GSSG-Red. Feeding MO resulted in lower (P <0.001) RBC and heart GSH-Px activities. In contrast, feeding B and BT resulted in lower GSH-Px in liver. The significant (P < 0.01) animal strain x fat source interaction obtained for liver GSH-Px activity indicated that SHR responded differently to polyunsaturated fatty acid feeding than their WKY counterparts. Diet-induced changes in tissue antioxidant status were tissue specific and did not affect the development of hypertension in SHR.

Addition of triglycerides with arachidonic acid or docosahexaenoic acid to infant formula has tissue- and lipid class-specific effects on fatty acids and hepatic desaturase activities in formula-fed piglets

The effects of including triglycerides with arachidonic [20:4(n-6)] or docosahexaenoic acid [22:6(n-3)] in formula on plasma chylomicron, LDL and HDL, liver, heart, kidney and brain (n-6) and (n-3) fatty acids were investigated in formula-fed piglets. Piglets were fed formula with (in % total fatty acids) 20% 18:2(n-6) and 2% 18:3(n-3) without or with 0.8% 20:4(n-6) or 0.3% 22:6(n-3) from birth to 18 d. The effects of adding 20:4(n-6) or 22:6(n-3) to the formula differed among different tissues and lipids, with the brain showing resistance to change. Piglets fed formula with 20:4(n-6) had significantly higher plasma, heart and kidney phospholipid and triglyceride, and liver triglyceride 20:4(n-6), but lower plasma and tissue phospholipid 18:2(n-6) than piglets fed formula without 20:4(n-6). Supplementation with 22:6(n-3), in contrast, had no effect on plasma or tissue 18:2(n-6). Higher 22:6(n-3) in liver phospholipid (30-92% greater) and triglyceride (200% greater) in piglets fed formula with 22:6(n-3) rather than without 22:6(n-3) was accompanied by lower 20:4(n-6) in liver phosphatidylethanolamine (mean +/- SEM, 8.6 +/- 0.4 and 10.5 +/- 0.4% fatty acids, respectively), but higher 20:4(n-6) in triglyceride (5.2 +/- 0.4 and 11.5 +/- 0.5%, respectively), and higher liver, heart and kidney phospholipid 20:5(n-3). These results indicate competitive interaction between dietary 20:4(n-6) and tissue 18:2(n-6), and between dietary 20:4(n-6) and tissue 20:5(n-3), rather than 22:6(n-3). The results also show that even at low intakes, dietary 22:6(n-3) or 20:4(n-6) supplementation alters the tissue phospholipid 20:4(n-6) to 20:5(n-3) balance. Studies on the physiologic effects of dietary 20:4(n-6) and 22:6(n-3) supplementation should consider the different sensitivity among tissues to dietary fatty acids.

Analysis of the putative role of 24-carbon polyunsaturated fatty acids in the biosynthesis of docosapentaenoic (22:5n-6) and docosahexaenoic (22:6n-3) acids

The recent literature on the putative involvement of a single cycle of peroxisomal beta-oxidation of 24:5n-6 and 24:6n-3 polyunsaturated fatty acids in the biosynthesis of the respective docosapentaenoic (22:5n-6) and docosahexaenoic (22:6n-3) fatty acids is critically reviewed. Present evidence suggests that in vitro data in support of the above proposition is an artifact of a low 2,4-dienoyl-CoA reductase activity due to depletion of NADPH resulting from incubation conditions. Kinetic studies with radiolabeled precursors in cell cultures have shown lower initial rates of labeling of 24:6n-3 than that of 22:6n-3, indicating that 24:6n-3 is an elongation product of 22:6n-3 rather than its precursor. Analysis of other literature data supports the proposal that 22:5n-6 and 22:6n-3 are synthesized in mitochondria via channeled carnitine-dependent pathways involving separate n-6- and n-3-specific desaturases. It is proposed that impaired peroxisomal function in some peroxisomal disorders is a secondary consequence of defective mitochondrial synthesis of 22:6n-3; moreover, some disorders of peroxisomal beta-oxidation show normal or increased 22:5n-6 concentrations, indicating that 22:5n-6 is synthesized by independent desaturases without peroxisomal involvement.

Comparative effects of alpha- and gamma-linolenic acids on rat liver fatty acid oxidation

It has been reported that both n-3 and n-6 octadecatrienoic acids can increase hepatic fatty acid oxidation activity. It remains unclear, however, whether different enzymes in fatty acid oxidation show a similar response to n-3 and n-6 octadecatrienoic acids. The activity of hepatic fatty acid oxidation enzymes in rats fed an oil mixture rich in alpha-linolenic acid (18:3n-3) and borage oil rich in gamma-linolenic acid (18:3n-6) was therefore compared to that in rats fed an oil mixture rich in linoleic acid (18:2n-6) and a saturated fat (palm oil) in this study. Linseed oil served as the source of 18:3n-3 for the oil mixture rich in this octadecatrienoic acid and contained 30.6% 18:3n-3 but not 18:3n-6. Borage oil contained 25.7% 18:3n-6 and 4.5% 18:3n-3. Groups of seven rats each were fed diets containing 15% various fats for 15 d. The oxidation rate of palmitoyl-CoA in the peroxisomes was higher in rats fed a fat mixture rich in 18:3n-3 (3.03 nmol/min/mg protein) and borage oil (2.89 nmol/min/mg protein) than in rats fed palm oil (2.08 nmol/min/mg protein) and a fat mixture rich in 18:2n-6 (2.15 nmol/min/mg protein). The mitochondrial palmitoyl-CoA oxidation rate was highest in rats fed a fat mixture rich in 18:3n-3 (1.93 nmol/min/mg protein), but no significant differences in this parameter were seen among the other groups (1.25-1.46 nmol/min/mg protein). Compared to palm oil and fat mixtures rich in 18:2n-6, a fat mixture rich in 18:3n-3 and borage oil significantly increased the hepatic activity of carnitine palmitoyltransferase and acyl-CoA oxidase. Compared to palm oil and a fat mixture rich in 18:2n-6, a fat mixture rich in 18:3n-3, but not fats rich in 18:3n-6, significantly decreased 3-hydroxyacyl-CoA dehydrogenase activity. Compared to palm oil and a fat mixture rich in 18:2n-6, borage oil profoundly decreased mitochondrial acyl-CoA dehydrogenase activity, but a fat mixture rich in 18:3n-3 increased it. 2,4-Dienoyl-CoA reductase activity was significantly lower in rats fed palm oil than in other groups. Compared to other fats, borage oil significantly increased delt3,delta2-enoyl-CoA isomerase activity. Activity was also significantly higher in rats fed 18:2n-6 oil than in those fed palm oil. It was confirmed that both dietary 18:3n-6 and 18:3n-3 increased fatty acid oxidation activity in the liver. These two dietary octadecatrienoic acids differ considerably, however, in how they affect individual fatty acid oxidation enzymes.

Effect of dietary docosahexaenoic acid on in vitro thermogenesis and fatty acid compositions of brown adipose tissue

Brown adipose tissue (BAT) is a major organ of nonshivering thermogenesis during cold acclimation, overfeeding, and nonthermal restraint stress. An increased unsaturation of fatty acids of membrane phospholipid in BAT has been shown to be closely associated with an enhanced function of this tissue as reported in other tissues. In the previous study, we found that among fatty acids detected, the n-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) in BAT phospholipid is the only fatty acid that altered concomitantly with a change in the in vitro thermogenic capacity for nonshivering thermogenesis of BAT from cold acclimated and restrained rats. To examine the effect of dietary DHA on fatty acid composition of phospholipid and in vitro BAT thermogenic activity, rats were fed a standard diet supplemented with purified DHA for 4 or 16 weeks. Dietary DHA for 4 or 16 weeks increased DHA level in BAT phospholipid, and it also decreased arachidonic acid. The unsaturation index increased and remained unchanged under DHA feeding for 4 and 16 weeks, respectively. In vitro thermogenic activity of BAT remained unchanged and decreased under dietary DHA for 4 and 16 weeks, respectively. These findings indicate that dietary DHA could increase DHA level in phospholipid of BAT, but it could not improve in vitro BAT thermogenic response.

On the effect of 2-deuterium- and 2-methyl-eicosapentaenoic acid derivatives on triglycerides, peroxisomal beta-oxidation and platelet aggregation in rats

A series of 2-substituted eicosapentaenoic acid (EPA) derivatives (as ethyl esters) have been synthesized and evaluated as hypolipidemic and antithrombotic agents in feeding experiments in rats. Repeated administration of purified 2-methyl-eicosapentaenoic acid and its deuterium analogues (all as ethyl esters) to rats resulted in a decrease in plasma triglycerides and high density lipoprotein cholesterol. The 2-methyl-EPA analogues were, apparently, four times more potent than EPA in inducing the triglyceride lowering effect. The 2-deuterium-2-methyl-EPA decreased plasma cholesterol level to approximately 40%. A moderate enlargement of the liver was observed in 2-methyl-EPA treated rats. This was accompanied with an acute reduction in the liver content of triglycerides and a stimulation of peroxisomal beta-oxidation and fatty acyl-CoA oxidase activity. The results suggest that the triglyceride-lowering effect of 2-methyl-EPA may be due to a reduced supply of fatty acids for hepatic triglyceride biosynthesis because of increased fatty acid oxidation. Platelet aggregation with ADP and A23187 was performed ex vivo in platelet-rich plasma, after administration of different doses of the EPA-derivatives for five days. EPA and 2,2-dideuterium EPA had no effect on ADP-induced aggregation, while 2-deuterium-, 2-methyl- and 2-deuterium-2-methyl EPA produced a biphasic effect, i.e. potentiation and inhibition at low (250 mg/day kg body weight) and higher doses (600-1300 mg/day kg body weight), respectively. A23187-induced platelet aggregation was affected in a similar way by feeding the 2-substituted EPA derivatives, except that 2-deuterium-2-methyl EPA had no effect relative to EPA itself and that the inhibition was far greater than that for ADP-induced aggregation (approximately 100% inhibition with 600 mg 2-methyl-EPA/day kg body weight). The ranking order of the EPA-derivatives to affect platelet aggregation and to cause hypolipidemia was different, suggesting different mechanisms. Our observations suggest that the effects of the EPA derivatives on platelet aggregation could be related to the degree of bulkiness around C2 and that an asymmetric substitution at C2 caused inhibition of platelet aggregation while a symmetric substitution did not. It is suggested that the bulky, asymmetric derivatives inhibit platelet aggregation by altering platelet membrane phospholipid packing.

Comparison of short- and long-term effects of different dietary fats on the hepatic uptake and metabolism of chylomicron remnants in rats

The uptake and metabolism of [14C]oleate-labelled chylomicron remnants derived from olive oil, maize oil, palm oil, fish oil or butter fat was investigated using perfused livers from rats fed on the corresponding fat-supplemented diet (providing 40% of the dietary energy) or a low-fat diet for 21 d. The percentage of added [14C]oleate-labelled remnant removed from the perfusate was similar for livers from rats fed on the fat-supplemented diets irrespective of the type of fat fed, whereas livers from rats fed on the low-fat diet removed more labelled fish oil and butter fat remnants than olive, maize or palm oil remnants. Following hepatic uptake in the fat-supplemented groups, the oxidation of [14C]oleate-labelled remnant lipid from maize oil, fish oil, and butter fat remnants was greater than that of the lipids from olive and palm oil remnants, although only the oxidation of lipids from maize and palm oil remnants was increased by prior fat-supplementation of the diet. In addition, the livers from rats fed on the fish-oil-supplemented diet incorporated more [14C]oleate-labelled remnant lipid into phospholipid compared with the livers from rats fed on the other fat-supplemented diets or the low-fat diets. These investigations show that both prior fat feeding and the composition of the fat fed, as well as the fatty acid composition of the chylomicron remnant particles themselves, influence the uptake and metabolism of chylomicron remnants by the liver.

Effects of highly purified eicosapentaenoic acid and docosahexaenoic acid on fatty acid absorption, incorporation into serum phospholipids and postprandial triglyceridemia

Fourteen healthy volunteers were randomly allocated to receive 4 g highly purified ethyl esters of eicosapentaenoic acid (EPA) (95% pure, n = 7) or docosahexaenoic acid (DHA) (90% pure, n = 7) daily for 5 wk in supplement to their ordinary diet. The n-3 fatty acids were given with a standard high-fat meal at the beginning and the end of the supplementation period. EPA and DHA induced a similar incorporation into chylomicrons which peaked 6 h after the meal. The relative uptake of EPA and DHA from the meal was > 90% compared with the uptake of oleic acid. During absorption, there was no significant elongation or retroconversion of EPA or DHA in total chylomicron fatty acids. The concentration of EPA decreased by 13% and DHA by 62% (P < 0.001) between 6 and 8 h after the meal. During the 5-wk supplementation period, EPA showed a more rapid and comprehensive increase in serum phospholipids than did DHA. DHA was retroconverted to EPA, whereas EPA was elongated to docosapentaenoic acid (DPA). The postprandial triglyceridemia was suppressed by 19 and 49% after prolonged intake of EPA and DHA, respectively, indicating that prolonged intake of DHA is equivalent to or even more efficient than that of EPA in lowering postprandial triglyceridemia. This study indicates that there are metabolic differences between EPA and DHA which may have implications for the use of n-3 fatty acids in preventive and clinical medicine.

Dose-Response Effect of Dietary Docosahexaenoic Acid on Fatty Acid Profiles of Serum and Tissue Lipids in Rats

The dose-response effects of dietary docosahexaenoic acid (22:6n-3, DHA) on the fatty acid profiles of total lipids of rat serum and tissues were investigated. Rats were fed diets containing graded levels of purified DHA at 0, 1.0, 3.4, and 8.7% of total energy in the diets for 2 weeks. It was found that each tissue had its own peculiar composition of fatty acids which differed markedly from that of circulating serum lipid. This composition was basically influenced dose-dependently by the dietary lipids with graded levels of DHA, but to different degrees in different tissues. Those of brain were most resistant and of heart most susceptible to dietary DHA.

Enhanced hepatic fatty acid oxidation and upregulated carnitine palmitoyltransferase II gene expression by methyl 3-thiaoctadeca-6,9,12,15-tetraenoate in rats

This study reports the effects of a novel polyunsaturated 3-thia fatty acid, methyl 3-thiaoctadeca-6,9,12,15-tetraenoate on serum lipids and key enzymes in hepatic fatty acid metabolism compared to a saturated 3-thia fatty acid, tetradecylthioacetic acid. Palmitic acid treated rats served as controls. Fatty acids were administered by gavage in daily doses of 150 mg/kg body weight for 10 days. The aim of the present study was: (a) To investigate the effect of a polyunsaturated 3-thia fatty acid ester, methyl 3-thiaoctadeca-6,9,12,15-tetraenoate on plasma lipids in normolipidemic rats: (b) to verify whether the lipid-lowering effect could be consistent with enhanced fatty acid oxidation: and (c) to study whether decreased activity of esterifying enzymes and diversion to phospholipid synthesis is a concerted mechanism in limiting the availability of free fatty acid as a substrate for hepatic triglyceride formation. Repeated administration of the polyunsaturated 3-thia fatty acid ester for 10 days resulted in a reduction of plasma triglycerides (40%), cholesterol (33%) and phospholipids (20%) compared to controls. Administration of polyunsaturated and saturated 3-thia fatty acids (daily doses of 150 mg/kg body weight) reduced levels of lipids to a similar extent and followed about the same time-course. Both mitochondrial and peroxisomal fatty acid oxidation increased (1.4-fold- and 4.2-fold, respectively) and significantly increased activities of carnitine palmitoyltransferase (CPT) (1.6-fold), 2,4-dienoyl-CoA reductase (1.2-fold) and fatty acyl-CoA oxidase (3.0-fold) were observed in polyunsaturated 3-thia fatty acid treated animals. This was accompanied by increased CPT-II mRNA (1.7-fold). 2,4-dienoyl-CoA reductase mRNA (2.9-fold) and fatty acyl-CoA oxidase mRNA (1.7-fold). Compared to controls, the hepatic triglyceride biosynthesis was retarded as indicated by a decrease in liver triglyceride content (40%). The activities of glycerophosphate acyltransferase, acyl-CoA: 1,2-diacylglycerol acyltransferase and CTP:phosphocholine cytidylyltransferase were increased. The cholesterol lowering effect was accompanied by a reduction in HMG-CoA reductase activity (80%) and acyl-CoA:cholesterol acyltransferase activity (33%). In hepatocytes treated with methyl 3-thiaoctadeca-6,9,12,15-tetraenoate, fatty acid oxidation was increased 1.8-fold compared to controls. The results suggest that treatment with methyl 3-thiaoctadeca-6,9,12,15-tetraenoate reduces plasma triglycerides by a decrease in the availability of fatty acid substrate for triglyceride biosynthesis via enhanced fatty acid oxidation, most likely attributed to the mitochondrial fatty acid oxidation. It is hypothesized that decreased phosphatidate phosphohydrolase activity may be an additive mechanism which contribute whereby 3-thia fatty acids reduce triglyceride formation in the liver. The cholesterol-lowering effect of the polyunsaturated 3-thia fatty acid ester may be due to changes in cholesterol/cholesterol ester synthesis as 60% of this acid was observed in the hepatic cholesterol ester fraction.

Polyunsaturated fatty acid suppression of hepatic fatty acid synthase and S14 gene expression does not require peroxisome proliferator-activated receptor alpha

Dietary polyunsaturated fatty acids (PUFA) induce hepatic peroxisomal and microsomal fatty acid oxidation and suppress lipogenic gene expression. The peroxisome proliferator-activated receptor alpha (PPARalpha) has been implicated as a mediator of fatty acid effects on gene transcription. This report uses the PPARalpha-deficient mouse to examine the role of PPARalpha in the PUFA regulation of mRNAs encoding hepatic lipogenic (fatty acid synthase (FAS) and the S14 protein (S14)), microsomal (cytochrome P450 4A2 (CYP4A2)), and peroxisomal (acyl-CoA oxidase (AOX)) enzymes. PUFA ingestion induced mRNAAOX (2.3-fold) and mRNACYP4A2 (8-fold) and suppressed mRNAFAS and mRNAS14 by >/=80% in wild type mice. In PPARalpha-deficient mice, PUFA did not induce mRNAAOX or mRNACYP4A2, indicating a requirement for PPARalpha in the PUFA-mediated induction of these enzymes. However, PUFA still suppressed mRNAFAS and mRNAS14 in the PPARalpha-deficient mice. Studies in rats provided additional support for the differential regulation of lipogenic and peroxisomal enzymes by PUFA. These studies provide evidence for two distinct pathways for PUFA control of hepatic lipid metabolism. One requires PPARalpha and is involved in regulating peroxisomal and microsomal enzymes. The other pathway does not require PPARalpha and is involved in the PUFA-mediated suppression of lipogenic gene expression.

Omega-3 and omega-6 fatty acids in the insulin resistance syndrome. Lipid and lipoprotein metabolism and atherosclerosis

Dietary fatty acids appear to be of significant importance for several of the most-common diseases in modern societies. To obtain more knowledge about the health consequences of dietary fatty acids, we depend upon a better understanding of the mechanisms of action of these fatty acids in vivo. With regard to the IRS, omega-3 PUFA may exert beneficial effects upon many of the associated pathophysiological metabolic changes. Omega-3 PUFA reduce fasting and postprandial TG, may improve insulin sensitivity (as shown in animal experiments), decrease platelet and leukocyte reactivity, alter immunological functions, and may slightly decrease blood pressure. Omega-3 PUFA may also beneficially influence vessel wall characteristics and blood rheology. Furthermore, both types of PUFA (omega-3 and omega-6) have been shown to inhibit cardiac arrhythmias in animals. The role of omega-3 PUFA in blood clotting and fibrinolysis still remains controversial, whereas omega-6 fatty acids may lead to increased oxidation of lipoproteins. Regardless of the effects on LDL oxidizability, both types of PUFA have shown beneficial effects on the development of atherosclerosis. As yet, little is known about the effect of specific omega-6 fatty acids with respect to the IRS. Potential adverse effects of dietary PUFA must not be neglected, but should be viewed in light of the beneficial effects of these agents.

Eicosapentaenoic acid and sulphur substituted fatty acid analogues inhibit the proliferation of human breast cancer cells in culture

Numerous studies have shown dietary fatty acids to influence the progression of several types of cancers. The purpose of the present investigation was to examine the influence of various types of fatty acids, including omega-3 fatty acids and a new class of hypolipidemic peroxisome proliferating fatty acid analogues, namely the 3-thia fatty acids, on MCF-7 human breast cancer cell growth. 3-thia fatty acids represent non-beta-oxidizable fatty acid analogues in which a sulphur atom substitutes for the beta-methylene group (3-position) in the saturated and unsaturated fatty acids. The effects of increasing concentrations of palmitic acid, tetradecylthioacetic acid (a 3-thia fatty acid), eicosapentaenoic acid, docosahexaenoic acid, and two 3-thia polyunsaturated fatty acids on the proliferation of MCF-7 cells, maintained in serum-free culture, were studied. At the highest concentration of fatty acid used (64 microM) tetradecylthioacetic acid was found to be the most effective of all fatty acids tested in inhibiting cell growth, whilst palmitic acid and docosahexaenoic acid had no significant effect on cell growth. Thus, of the two dietary polyunsaturated omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid, only eicosapentaenoic acid possesses an inhibitory effect on the proliferation of MCF-7 cells. In all cases the inhibitory effect of the fatty acid was found to be reversible. Tetradecylthioacetic acid has been shown to be a potent peroxisome proliferator. It was, therefore, hypothesized that tetradecylthioacetic acid may inhibit the human MCF-7 cell growth by increasing the level of oxidative stress within the cell. However, use of agents which modify the cell's protective apparatus against oxidative stress had no influence on the inhibitory effect of tetradecylthioacetic acid. These experiments indicate that tetradecylthioacetic acid inhibits cell growth by mechanisms which may be independent of oxidative status.

Increased hepatic beta-oxidation of docosahexaenoic acid, elongation of eicosapentaenoic acid, and acylation of lysophosphatidate in rats fed a docosahexaenoic acid-enriched diet

Rats were fed a diet supplemented with corn oil (n-3 deficient), soy oil, or a mixture containing 8% 22:6n-3 ethyl ester for 6 wk. The hepatic capacities for the beta-oxidation and synthesis of 22:6n-3, in addition to the acylation of lysophosphatidate, were tested in vitro. In rats that were fed a 22:6n-3-enriched diet, both the beta-oxidation of 22:6n-3 and elongation of 20:5n-3 were enhanced compared to those in rats fed the other diets. Acylation of lysophosphatidate was also enhanced in rats fed a 22:6n-3-enriched diet, while the rate of dephosphorylation of phosphatidate was not changed. The amount of 22:6n-3 in the liver was much less than that consumed in a docosahexaenoic acid-enriched diet. These results suggest that a significant amount of dietary 22:6n-3 was degraded via beta-oxidation, and that a portion of the retroconverted 20:5n-3 was recycled for the synthesis of 22:6n-3. The recycling of 20:5n-3 might contribute to the low level of 22:6n-3 in rats fed an n-3-deficient diet.

Incorporation of long-chain n-3 fatty acids in tissues and enhanced bone marrow cellularity with docosahexaenoic acid feeding in post-weanling Fischer 344 rats

We wanted to examine the effects of an oil rich in docosahexaenoic acid (DHA), without eicosapentaenoic acid, on the composition of membrane phospholipid in a variety of tissues. Our in vitro studies had previously shown that DHA could modify glucose and nucleoside transport in cells in culture and also increase selectivity of the nucleoside drug, arabinosylcytosine (araC) toward tumor cells. Here we wanted to examine what effect DHA supplementation would have in the whole animal in terms of the chemosensitivity of normal bone marrow, the dose-limiting tissue during chemotherapy, to araC. The purpose was to determine whether fatty acid supplementation might be useful as an adjuvant to chemotherapy. We fed diets containing 5% (w/w) low fat-corn oil (LF-CO group), 10% moderate fat-safflower oil (MF-SO group), or 10% DHASCO (MF-DHA group) to weanling Fischer 344 rats for 8-9 wk. Feed intake and growth were not different between the different diets. Similarly, treatment of animals with the chemotherapeutic drug araC did not differentially affect growth, feed intake, or tissue fatty acid composition for the different diet groups. Fatty acid compositions of bone marrow, liver, red blood cells, plasma phospholipid and triglyceride, as well as skeletal and cardiac muscle, were substantially different between the dietary groups. The DHASCO oil contained 46% DHA (22:6n-3) and resulted in profound incorporation of DHA in all tissues examined. The most dramatic response was seen in skeletal muscle of MF-DHA fed animals where DHA represented 46% of membrane phospholipid fatty acids. This is likely to have consequences to muscle function. Although DHASCO contains a similar level of saturated fatty acids (42%), few differences in saturates were noted between the various dietary groups for most of the tissues examined. Both LF-CO and MF-SO diets were hypercholesterolemic, and the LF-CO was also hypertriglyceridemic compared to the chow-fed animals. Animals fed the MF-DHA diet had the lowest triglyceride levels of any of the treatment groups and cholesterol levels comparable to chow-fed animals. MF-DHA had substantially higher numbers of colony-forming units-granulocyte macrophage (CFU-GM) as reflected in a twofold higher bone marrow cellularity than either chow or LF-CO animals, suggesting expansion of the bone marrow compartment with DHA feeding. Although higher than LF-SO, the number of CFU-GM in MF-SO animals was not significantly higher than animals fed chow. Bone marrow from LF-CO animals appeared to be more resistant to araC treatment than either MF group. Thus, DHA, fed as DHASCO, has advantages over low or moderate n-6 diets and chow as it is has both hypolipidemic- and bone marrow-enhancing properties in weanling Fischer 344 rats. This suggests that DHA supplementation may be useful in adjuvant chemotherapy.

Omega-3 fatty acid supplementation does not improve maximal aerobic power, anaerobic threshold and running performance in well-trained soccer players

In a randomized, placebo-controlled study the effect of 10 weeks of supplementation with either 5.2 g of a concentrated fish oil triglyceride (Triomar) enriched in omega-3 fatty acids (1.60 g/day EPA and 1.04 g/ day DHA) or 5.2 g corn oil (serving as placebo) on maximal aerobic power, anaerobic threshold and running performance was assessed in 28 well-trained male soccer players (18-35 years). Supplements were given as 650-mg capsules. Capsule assignment was randomized to one omega-3 group (n = 15), given eight Triomar capsules per day, and one placebo group (n = 13), given eight capsules of corn oil per day. During the 10-week supplementation period the subjects maintained their usual diets and training regimes. Red blood cell (RBC) osmotic fragility, triglycerides and fatty acid composition in plasma were assessed before and after the supplementation period. The pre- and post-supplementation tests of maximal aerobic power, anaerobic power and running performance showed no significant difference between the two groups. Subjects in the omega-3 group had significantly reduced plasma triglycerides, rose EPA (175%) and DHA (40%) in the total lipid fraction of plasma after supplementation. RBC osmotic fragility did not change. In conclusion, the results do not support the hypothesis that endurance athletes can improve maximal aerobic performance by omega 3-fatty acid supplementation.

Dietary docosahexaenoic acid has little effect on peroxisomes in healthy mice

NMRI mice were fed diets supplemented with 0.05, 0.2, or 2% (w/w) docosahexaenoic acid (DHA), a polyunsaturated fatty acid present in fish oil, for 3 d, 3 wk, or 3 mon. The doses of DHA were chosen to supply the mice with concentrations of DHA which approximate those that have been reported to be beneficial to patients with peroxisomal disease. Diets containing 0.05 or 0.2% DHA did not change hepatic, myocardial, and renal catalase (EC 1.11.1.6) activity except for a slight but significant increase (to 120%) in myocardial catalase activity in mice treated with the 0.05% DHA diet for 3 mon. A diet with 2% DHA induced myocardial catalase activity to 150% after both 3 d and 3 wk of administration. In the liver of mice fed this diet for 3 wk, hepatic catalase activity was increased to 140% while no induction of palmitoyl-CoA oxidase (EC 1.3.99.3), urate oxidase (EC 1.7.3.3), and L-alpha-hydroxyisovalerate oxidase (EC 1.1.3.a) was observed. With the light microscope, no changes in peroxisomal morphology were visually evaluated in catalase stained sections of liver, myocardium, and kidney of mice fed either diet. Our results show that in healthy mice a low dietary DHA dose (< 0.2%; this corresponds to a dose prescribed to peroxisomal patients) has no effect on several hepatic peroxisomal H2O2-producing enzymes, including the rate-limiting enzyme of the peroxisomal fatty acid beta-oxidation. This may indicate that such a DHA dose will not add a strong load on the often disturbed fatty acid metabolism in the liver of patients with peroxisomal disorders.

The peroxisome proliferator activated receptors (PPARS) and their effects on lipid metabolism and adipocyte differentiation

The three types of peroxisome proliferator activated receptor (PPAR), alpha, beta (or delta), and gamma, each with a specific tissue distribution, compose a subfamily of the nuclear hormone receptor gene family. Although peroxisome proliferators, including fibrates and fatty acids, activate the transcriptional activity of these receptors, only prostaglandin J2 derivatives have been identified as natural ligands of the PPAR gamma subtype, which also binds thiazolidinedione antidiabetic agents with high affinity. Activated PPARs heterodimerize with RXR and alter the transcription of target genes after binding to specific response elements or PPREs, consisting of a direct repeat of the nuclear receptor hexameric DNA core recognition motif spaced by one nucleotide. The different PPARs can be considered key messengers responsible for the translation of nutritional, pharmacological and metabolic stimuli into changes in the expression of genes, more specifically those genes involved in lipid metabolism. PPAR alpha is involved in stimulating beta-oxidation of fatty acids. In rodents, a PPAR alpha-mediated change in the expression of genes involved in fatty acid metabolism lies at the basis of the phenomenon of peroxisome proliferation, a pleiotropic cellular response, mainly limited to liver and kidney and which can lead to hepatocarcinogenesis. In addition to their role in peroxisome proliferation in rodents, PPAR is also involved in the control of HDL cholesterol levels by fibrates and fatty acids in rodents and humans. This effect is, at least partially, based on a PPAR-mediated transcriptional regulation of the major HDL apolipoproteins, apo A-I and apo A-II. The hypotriglyceridemic action of fibrates and fatty acids also involves PPARs and can be summarized as follows: (1) an increased lipolysis and clearance of remnant particles, due to changes in LPL and apo C-III levels, (2) a stimulation of cellular fatty acid uptake and their conversion to acyl-CoA derivatives by the induction of FAT, FATP and ACS activity, (3) an induction of fatty acid beta-oxidation pathways, (4) a reduction in fatty acid and triglyceride synthesis, and finally (5) a decrease in VLDL production. Hence, both enhanced catabolism of triglyceride-rich particles as well as reduced secretion of VLDL particles are mechanisms that contribute to the hypolipidemic effect of fibrates and FFAs. Whereas for PPAR beta no function so far has been identified, PPAR gamma triggers adipocyte differentiation by inducing the expression of several genes critical for adipogenesis.

Eicosapentaenoic acid, but not docosahexaenoic acid, increases mitochondrial fatty acid oxidation and upregulates 2,4-dienoyl-CoA reductase gene expression in rats

The aim of the present study was to investigate whether eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) was responsible for the triglyceride-lowering effect of fish oil. In rats fed a single dose of EPA as ethyl ester (EPA-EE), the plasma concentration of triglycerides was decreased at 8 h after acute administration. This was accompanied by an increased hepatic fatty acid oxidation and mitochondrial 2,4-dienoyl-CoA reductase activity. The steady-state level of 2,4-dienoyl-CoA reductase mRNA increased in parallel with the enzyme activity. An increased hepatic long-chain acyl-CoA content, but a reduced amount of hepatic malonyl-CoA, was obtained at 8 h after acute EPA-EE treatment. On EPA-EE supplementation, both EPA (20:5n-3) and docosapentaenoic acid (DPA, 22:5n-3) increased in the liver, whereas the hepatic DHA (22:6n-3) concentration was unchanged. On DHA-EE supplementation retroconversion to EPA occurred. No statistically significant differences were found, however, for mitochondrial enzyme activities, malonyl-CoA, long-chain acyl-CoA, plasma lipid levels, and the amount of cellular fatty acids between DHA-EE treated rats and their controls at any time point studied. In cultured rat hepatocytes, the oxidation of [1-14C]palmitic acid was reduced by DHA, whereas it was stimulated by EPA. In the in vivo studies, the activities of phosphatidate phosphohydrolase and acetyl-CoA carboxylase were unaffected after acute EPA-EE and DHA-EE administration, but the fatty acyl-CoA oxidase, the rate-limiting enzyme in peroxisomal fatty acid oxidation, was increased after feeding these n-3 fatty acids. The hypocholesterolemic properties of EPA-EE may be due to decreased 3-hydroxy-3-methylglutaryl-CoA reductase activity. Furthermore, replacement of the ordinary fatty acids, i.e., the monoenes (16:1n-7, 18:1n-7, and 18:1n-9) with EPA and some conversion to DPA concomitant with increased fatty acid oxidation is probably the mechanism leading to changed fatty acid composition. In contrast, DHA does not stimulate fatty acid oxidation and, consequently, no such displacement mechanism operates. In conclusion, we have obtained evidence that EPA, and not DHA, is the fatty acid primarily responsible for the triglyceride-lowering effect of fish oil in rats.

Effects of fish oil and safflower oil emulsions on diet-inducedhepatic steatosis in rats receiving total parenteral nutrition

This study was conducted to investigate the effects of fish oil and safflower oil emulsions in total parenteral nutrition (TPN) solutions on diet-induced hepatic steatosis. Rats were divided into a control group (C, n = 6) and four experimental groups (A, B, S, F, n = 11 approximately 14). The control group was fed a chow diet whereas the experimental groups received a high fat (15%, w/w) diet containing 0.1% (w/w) cholesterol. Group A received the high fat diet for 4 weeks, and was killed at the end of the fourth week to ensure that hepatic steatosis had occurred. Groups S and group F received TPN with safflower oil or fish oil emulsions, respectively, for 1 week following experimental diet feeding for 4 weeks. Group B was fed a limited amount of the high fat diet, without cholesterol, for 1 week following 4 weeks of experimental diet in order to maintain the same body weight and cholesterol intake as the TPN groups. Diet-induced hepatic steatosis was observed in the experimental groups. Fat deposition was reversed when the total caloric and cholesterol intake was reduced. Fish oil infusion ameliorated the severity of hepatic steatosis, whereas safflower oil had no effect on liver fat deposition. These results suggest that TPN with fish oil emulsions may be beneficial to patients with diet-induced hepatic steatosis.

Docosahexaenoic acid therapy in docosahexaenoic acid-deficient patients with disorders of peroxisomal biogenesis

A patient with classic Zellweger syndrome was treated with docosahexaenoic acid ethyl ester (DHA-EE) for three months. Five other patients with Zellweger variants (four of them less than one-year-old and a five-year-old) were treated with DHA-EE until normalization of the DHA levels in erythrocytes. When arachidonic acid (AA) concentration decreased, AA was added to the diet. Thereafter, a combined treatment with DHA plus AA followed, in a variable proportion that allowed the high levels of DHA in erythrocytes to be maintained. In the patient with Zellweger syndrome, DHA therapy produced an increase in plasmalogen and a decrease in 26:0 and 26:1. No clear clinical improvement could be detected in this patient during the short period of treatment with DHA-EE. The most consistent clinical effect produced by DHA therapy in the other patients with disorders of peroxisomal biogenesis was visual improvement, even in those patients that were virtually blind before the treatment. In general, the developmental curve began to accelerate. The infants became more alert, acquired better visual and social contact and muscular tone improved, with the beginning of good head control. The liver tests tended to normalize and some patients showed a reduction of hepatomegaly. All these favorable changes occurred when the patients were taking the DHA-EE alone. In some of the patients, muscular tone seemed to improve further after introducing AA supplements. From the biochemical point of view, the plasmalogen levels increased in most cases in erythrocytes, and the two ratios 26:0/22:0 and 26:1/22:0 decreased in plasma. In some patients there was a tendency for 26:1 to increase in plasma and for 18:0 plasmalogen to decrease in erythrocytes when AA was introduced in the diet. The significance of these findings remains to be elucidated, but they stress the importance of strict monitoring and control of the polyunsaturated fatty acids status during DHA therapy.

Control of endothelial leukocyte adhesion molecules by fatty acids

Dietary balance of long-chain fatty acids (FA) may influence human susceptibility to pathological processes which involve the interaction of leukocytes with vascular endothelium, such as atherogenesis and inflammation. Such interaction is largely mediated by the de novo or increased expression of endothelial leukocyte adhesion molecules on vascular endothelial cells, able to tether and stably bind leukocytes onto the vessel wall, and by the production of leukocyte chemoattractants. Endothelial cells do not normally support high levels of leukocyte adhesion. They do so, however, when exposed to a number of stimuli, such as oxidized low density lipoprotein bacterial lipopolysaccharides, and inflammatory cytokines, which induce phenotypic changes generally referred to as "endothelial activation." We compared various FA in their ability to modulate endothelial activation by cytokines. FA included linoleic, arachidonic, oleic, eicosapentaenoic and, docosa-hexaenoic acid (DHA) as representatives of the n-6, n-3 polyunsaturated FA and of the monounsaturated FA. The n-3 FA DHA, and, to a lesser extent, oleate, at nutritionally compatible concentrations, were able to reduce endothelial expression of Vascular Cell and Adhesion Molecule-1 (VCAM-1). In further studies, DHA dose- and time-dependently reduced also the expression of E-selectin, Intercellular Adhesion Molecule-1, interleukin (IL)-6 and IL-8, in response to IL-1, IL-4, tumor-necrosis factor, or bacterial endotoxin. The magnitude of this effect paralleled its incorporation into cellular phospholipids. Also, coordinate with reduced surface adhesion molecule expression, DHA reduced the adhesion of human monocytes and of monocytic U937 cells to cytokine-stimulated endothelial cells. These effects were accompanied by a quantitatively consistent reduction in VCAM-1 mRNA, indicating a pretranslational control of adhesion molecule gene expression. These novel properties of FA as modulators of endothelial activation may help to explain the influence of dietary FA intake on atherogenesis and inflammation.

Chronic administration of eicosapentaenoic acid and docosahexaenoic acid as ethyl esters reduced plasma cholesterol and changed the fatty acid composition in rat blood and organs

Fish oils rich in n-3 fatty acids have been shown to decrease plasma lipid levels, but the underlying mechanism has not yet been elucidated. This investigation was performed in order to further clarify the effects of purified ethyl esters of eicosapentaenoic acid (EPA-EE) and docosahexaenoic acid (DHA-EE) on lipid metabolism in rats. The animals were fed EPA-EE, DHA-EE, palmitic acid, or corn oil (1 g/kg/d) by orogastric intubation along with a chow background diet for three months. At the end the animals were sacrificed. Plasma and liver lipids were measured, as well as lipid-related enzyme activities and mRNA levels. The fatty acid composition of plasma and different tissues was also determined. This study shows that, compared to the corn oil control, EPA-EE and DHA-EE lowered plasma cholesterol level, whereas only EPA-EE lowered the amount of plasma triacylglycerol. In liver peroxisomes, both EE preparations increased fatty acyl-CoA oxidase FAO activities, and neither altered 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase activities. In liver microsomes, EPA-EE raised HMG-CoA reductase and acyl-CoAicholesterol acyltransferase activities, whereas DHA-EE lowered the former and did not affect the latter. Neither product altered mRNA levels for HMG-CoA reductase, low density lipoprotein-receptor, or low density lipoprotein-receptor related protein. EPA-EE lowered plasma triacylglycerol, reflecting lowered very low density lipoprotein secretion, thus the cholesterol lowering effect in EPA-EE-treated rats may be secondary to the hypotriacylglycerolemic effect. An inhibition of HMG-CoA reductase activity in DHA-EE treated rats may contribute to the hypocholesterolemic effect. The present study reports that 20:5n-3, and not 22:6n-3, is the fatty acid primarily responsible for the triacylglycerol lowering effect of fish oil. Finally, 20:5n-3 was not converted to 22:6n-3, whereas retroconversion of 22:6n-3 to 20:5n-3 was observed.

Effects of clofibrate on lipids and fatty acids of mouse liver

Clofibrate administration significantly altered the amount and fatty acid composition of lipids in mouse liver. The net content of phospholipids (PL) increased and that of triacylglycerols (TG) decreased concomitantly with liver enlargement in mice treated for two weeks with this drug (0.5% w/w in the food). The highest increase among PL was in phosphatidylcholine; other components either showed lower increases or, as in the case of sphingomyelin and the plasmalogens, decreased. In all lipid classes the treatment resulted in altered ratios between major saturates, between saturates and monoenes, and between major polyenes. Among these, 20:3n-6 and 22:5n-3 increased several-fold, and the 20:3n-6/20:4n-6 and 22:5n-3/22:6n-3 ratios increased due to a more active formation of the precursors than of the corresponding products. This change affected all glycerolipid classes. Liver sphingomyelin showed a relative enrichment in monoenoic fatty acids like 22:1 and 24:1, caused by a net decrease in the amount of saturates, particularly 22:0 and 24:0. The stimulated membrane proliferation imposed by clofibrate must increase phospholipid synthesis and, hence, the need for fatty acids. The results suggest that these demands are met mostly by TG acyl groups, either directly or after oxidation/desaturation processes. This was apparently the case for the polyenoic fatty acids of the n-6 and n-3 series. The longer chain (C22 and C24) components decreased, suggesting that their oxidation was stimulated to provide part of the required (C20 and C22) polyenes.

Effects of fat emulsions with different fatty acid composition on plasma and hepatic lipids in rats receiving total parenteral nutrition

Effects of different fatty acids on the development of hepatic steatosis were studied in rats receiving total parenteral nutrition (TPN). 65 rats, with internal jugular catheters, were divided into one control group (n = 8), and four experimental groups (n = 13-15 each). The control group was fed a chow diet and all experimental groups received TPN. TPN provided 300 kcal/kg/day with 40% of the non-protein energy provided as fat. All TPN solutions were isonitrogenous and identical in nutrient composition except for the fatty acid composition of the fat emulsion. Four kinds of fat emulsions rich in: 1) medium chain fatty acids (C8:0,C10:0), 2) oleic acid (C18:1 n-9), 3) linoleic acid (C18:2 n-6), 4) eicosapentaenoic acid (C20:5 n-3)/docosahexaenoic acid (C22:6 n-3), were used. These fat emulsions were prepared with: 1) a mixture of medium chain triglycerides (MCT) and soybean oil (9:1), 2) olive oil, 3) safflower oil, 4) fish oil, respectively. The results of the study demonstrated a higher hepatic lipid content in the olive oil and safflower oil groups than in the control group, whereas no significant difference was seen between the MCT and control groups. Also, no difference was observed between the fish oil and control groups. With regard to the plasma lipids, the MCT group and olive oil group produced hyperlipidaemia. The plasma of the safflower oil and fish oil groups, however, had a low lipid concentration comparable to the control group. These results suggest that TPN with a fat emulsion prepared with fish oil does not cause hyperlipidaemia nor induce hepatic steatosis in normal rats.

Effect of troglitazone (CS-045) and bezafibrate on glucose tolerance, liver glycogen synthase activity, and beta-oxidation in fructose-fed rats

To clarify the relationship between lipid and glucose metabolism abnormalities in fructose-fed rats, we examined whether an improvement of insulin sensitivity by troglitazone (CS-045) or a decrease in plasma lipids by bezafibrate affects the relationship between serum levels of lipid and glucose. In addition, we also examined changes in liver glycogen metabolism and beta-oxidation in fructose-fed rats. Troglitazone ameliorated fasting hyperlipidemia, hyperglycemia, and hyperinsulinemia. In addition, it augmented glycogen synthase activity by 53%, and decreased the mitochondrial palmitic acid beta-oxidation rate and ketone body production rate by 27% and 55%, respectively. However, hyperglycemia and liver glycogen synthase activity were not improved by bezafibrate treatment despite a marked reduction of serum triglyceride (TG) levels resulting from a 1.76-fold increase in mitochondrial oxidation and a 2.04-fold increase in hepatic ketone body production. These results suggest that abnormalities in glucose and lipid metabolism in fructose-fed rats, which are ameliorated by troglitazone, may be closely linked to reduced glycogen synthase activity in the liver.

Effect of marine oils supplementation on coagulation and cellular activation in whole blood

A study was performed to explore the effects of supplemental intake of various marine oils known to be part of the Eskimo diet. Healthy men and women (134) were randomly selected to consume 15 mL/d of oil from blubber of seal, cod liver, seal/cod liver, blubber of Minke whale, or no oil for ten weeks. Total cholesterol was unchanged in the oil groups, whereas high density lipoprotein cholesterol increased 7% in the seal/cod liver oil (CLO) group (P < 0.05) and 11% in the whale oil group (P < 0.005). Triacylglycerol was significantly reduced in the CLO group only. The concentration of prothrombin fragment 1 + 2 was reduced 25% (P < 0.05) after whale oil supplementation. No change in fibrinogen or factor VIIc was detected. Tumor necrosis factor generation in lipopolysaccharide (LPS)-stimulated blood was 30% reduced after whale oil (P < 0.05), but was unaffected by intake of seal or CLO. The LPS-induced tissue factor activity in monocytes was reduced to a significant degree only in the seal/CLO group (34%) and whale oil group (35%) (P < 0.05). The most dramatic change in thromboxane B2 in LPS-stimulated blood was seen after whale oil intake with 44% reduction (P < 0.01). Supplementation of a regular diet with a combination of seal oil and CLO and especially with whale oil seems to have beneficial effects on several products thought to be associated with cardiovascular and thrombotic diseases.

Effect of long-chain mono-unsaturated and n-3 polyunsaturated fatty acids on postprandial blood and liver lipids in rats

The effects on blood and liver lipids after feeding rats with concentrated fractions from fish oil consisting of mono-unsaturated fatty acids (80% C20:1 and 22:1) or n-3 polyunsaturated fatty acids (85% C20:5 and 22:6 n-3) were examined. Mono-unsaturated fat had no effects on plasma triacylglycerol, total cholesterol phospholipids or unesterified fatty acid as compared to controls (lard). However, n-3 polyunsaturated fatty acid-fed animals showed a significant decrease in plasma triacylglycerol (74%), phospholipids (40%) and unesterified fatty acids (52%). The concentrated fractions had no effects on liver lipids. While the n-3 diet increased peroxisomal beta-oxidation 2.5-fold, there was only a slight increase with the mono-unsaturated diet. The fatty acid composition in plasma and liver phospholipids was changed with the various diets; 20:4 n-6 was significantly reduced in plasma and liver with the mono-unsaturated diet, and with the n-3 diet in liver. The mono-unsaturated diet, and especially the n-3 diet, increased the 20:5 n-3 level in both plasma and liver. Our results indicate that long-chain mono-unsaturated fatty acids in fish oil do not change the levels of plasma lipids. The beneficial role of fish oil on the level of blood lipids, may therefore be mostly attributed to the effects of long-chain n-3 fatty acids. However, the low 20:4 n-6 and high 20:5 n-3 levels in plasma and liver phospholipids with the concentrated mono-unsaturated fatty acid diet may be of importance for a favourable haemostatic balance with regard to cardiovascular diseases.

Dietary fish oil and cytochrome P-450 monooxygenase activity in rat liver and kidney

Lauric acid hydroxylation and aminopyrine N-demethylation were studied in kidney and liver microsomes from rats treated with fish oil. Different doses of fish oil containing 20% eicosapentaenoic acid and 10% docosahexaenoic acid were provided daily to the rats for seven days. In all the groups studied, the lauric acid metabolism was higher in kidney microsomes and the aminopyrine metabolism in the liver microsomes. Although no effect on the renal cytochrome P-450 concentration was detectable, all four fish oil doses increased the hepatic concentration of cytochrome P-450 by a mean 27%. The higher fish oil doses used increased the renal and hepatic microsomal metabolism of aminopyrine. The lauric acid metabolism was increased by fish oil only in the liver. Fish oil, a known inducer of fatty acid peroxisomal beta-oxidation, also induced microsomal activity. These results show that liver and kidney respond in different ways to dietary factors such as fish oil. In addition, our study would suggest that fish oil increased the activity of two different families of liver cytochrome P-450. The activity of kidney lauric acid 11- and 12-hydroxylation, however, was not modulated by fish oil.

Peroxisomes in mice fed a diet supplemented with low doses of fish oil

The influence of low dietary doses (0.1 and 0.8% w/w) of a commercial fish oil preparation on peroxisomes in normal mice was studied and compared to the known strong inductive effects of high (10%) fish oil diets. Low fish oil doses were chosen to supply the mice with a concentration of docosahexaenoic acid, which was beneficial to patients with a peroxisomal disease. Peroxisomes were evaluated by cytochemical, morphometric, and enzymological techniques. The 0.1% fish oil diet had no effect on peroxisomes in liver, heart, and kidney even after prolonged treatment. The 0.8% diet did not change the peroxisomal number nor the catalase (EC 1.11.1.6) activity in the liver. Hepatic peroxisomal beta-oxidation, however, was increased by 50% after 14 d. This was accompanied by reduced peroxisomal size. The 0.8% diet also caused a small increase (+25%) in myocardial catalase activity. No effect was observed in kidneys. Our results indicate that in mice a low (< 0.8%) dietary fish oil dose has no or only a slight effect on hepatic peroxisomal beta-oxidation. This may be of particular interest to patients with a peroxisomal fatty acid beta-oxidation defect and who display a severe deficiency of docosahexaenoic acid--diets supplemented with low fish oil doses will improve the docosahexaenoic acid level without adding a strong load to the disturbed fatty acid metabolism.

Enteral feeding a structured lipid emulsion containing fish oil prevents the fatty liver of sepsis

Fish oils (FO) have been shown to reduce plasma triglycerides (TG). In this study we evaluated whether enteral feeding with a structured lipid emulsion (SLE) containing FO and medium-chain triglycerides (MCT) would prevent the hypertriglyceridemia and fatty infiltration of the liver that develops during sepsis. For five days, male Lewis rats (275-300 g) were fed intragastrically a nutritionally complete diet containing a SLE or a similar diet with a soybean oil emulsion (SOE) in place of the SLE. On the fifth day, sepsis was induced by intravenously injecting 8 x 10(7) live Escherichia coli colonies/100 g b.w.; 24 h later the control SLE, septic SLE, control SOE, and septic SOE rats were sacrificed. Diet, but not treatment, had a significant effect on serum TG and free fatty acids (FFA). Feeding the SLE reduced the plasma FFA of the control and septic rats by more than 50% in comparison to both control and septic rats fed the SOE. Soleus muscle activity of lipoprotein lipase from the septic SLE rats was 44% higher than the control SLE rats. Soleus muscle from the septic SLE rats also had a twofold greater activity of lipoprotein lipase than the septic SOE rats. TG did not accumulate in the livers of the septic rats fed SLE when compared to the control SLE rats and the rats fed the SOE. Livers from the septic rats fed the SLE had a third of the TG that were present in the livers from the septic rats fed the SOE.(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosapentaenoic acid causes transient accumulation of lipids in rat myocardium

Rats were given eicosapentaenoic acid (EPA) or palmitic acid (PALM) up to 15 days, and control animals were given carboxymethylcellulose. All suspensions which were given by gastric intubation contained tocopherol. Heart triacylglycerols, heart cholesterol and heart phospholipids significantly increased after one day of EPA treatment, but they were normalized within 15 days. Both after 2 and 10 days of treatment with palmitic acid the heart triacylglycerols were significantly greater than control. The heart cholesterol and heart phospholipids were significantly greater than control after 10 days of treatment with palmitic acid. Total carnitine palmitoyltransferase (CPT) activity in heart was significantly greater in rats treated with EPA for 15 days compared to control, but treatment with palmitic acid had no effect. The fatty acyl-CoA oxidase activity was greater in rats treated with EPA for 15 days and palmitic acid for 10 days compared to control. The fractional volume of lipid droplets in myocardial cells was calculated from electronmicrographs and was 0.112 +/- 0.016% after 1 day of EPA treatment compared to 0.035 +/- 0.016% in the control group. After 5 and 15 days the fractional volume was the same as control. The fractional volume of lipid droplets in rats treated with palmitic acid for 10 days was 0.120 +/- 0.023%. Treatment with EPA caused an immediate accumulation of lipids and lipid droplets in the rat heart which after few days normalized in parallel with an increased activity of total CPT in the heart.

Antithrombotic activity of a symmetrical triglyceride with eicosapentaenoic acid and gamma-linolenic acid in guinea pig mesenteric microvasculature

The antithrombotic effect of a synthetic symmetrical triglyceride having eicosapentaenoic acid (EPA) at positions 1 and 3, and gamma-linolenic acid (GLA) at position 2 was investigated. Administration of the triglyceride significantly increased thrombus formation time and thrombotic occlusion time induced by light irradiation and a fluorescent dye in guinea pigs after 14 days administration compared to that of soybean oil. The antithrombotic effect of the triglyceride was similar to that of EPA ethyl ester. Administration of the triglyceride increased GLA, dihomo-gamma-linolenic acid (DGLA) and EPA contents in plasma and the liver, and the ratio of DGLA to arachidonic acid. These results might be responsible for this antithrombotic effect.