Pathway of alpha-linolenic acid through the mitochondrial outer membrane in the rat liver and influence on the rate of oxidation. Comparison with linoleic and oleic acids

Long Chain Fatty Acids Mediate Hepatic Metabolic Flux in Preruminating Dairy Calves Fed Flaxseed Oil, High Oleic Soybean Oil, or Milk Fat

Nutrition and physiological state affect hepatic metabolism. Our objective was to determine if feeding flaxseed oil (∼50% C18:3n-3 cis), high oleic soybean oil (∼70% C18:1 cis-9), or milk fat (∼50% C16:0) alters hepatic expression of PC, PCK1, and PCK2 and the flow of carbons from propionate and pyruvate into the TCA cycle in preruminating calves. Male Holstein calves (n = 40) were assigned to a diet of skim milk with either: 3% milk fat (MF; n = 8), 3% flaxseed oil (Flax; n = 8), 3% high oleic soybean oil (HOSO; n = 8), 1.5% MF + 1.5% high oleic soybean oil (MF-HOSO; n = 8), or 1.5% MF + 1.5% flaxseed oil (MF-Flax; n = 8) from d 14 to d 21 postnatal. At d 21 postnatal, a liver biopsy was taken for gene expression and metabolic flux analysis. Liver explants were incubated in [U-13C] propionate and [U-13C] pyruvate to trace carbon flux through TCA cycle intermediates or with [U-14C] lactate, [1-14C] palmitic acid, or [2-14C] propionate to quantify substrate oxidation to CO2 and acid soluble products. Compared with other treatments, plasma C18:3n-3 cis was 10 times higher and C18:1 cis-9 was 3 times lower in both flax (Flax and MF-Flax) treatments. PC, PCK1, and PCK2 expression and flux of [U-13C] pyruvate as well as [U-13C] propionate were not different between treatments. PC expression was negatively correlated with the enrichment of citrate M+5 and malate M+3, and PCK2 was negatively correlated with citrate M+5, suggesting that when expression of these enzymes is increased, carbon from pyruvate enters the TCA cycle via PC mediated carboxylation, and then OAA is converted to phosphoenolpyruvate via PCK2. Acid soluble product formation and PC expression were reduced in HOSO (MF-HOSO and HOSO) treatments compared with flax (MF-Flax and Flax), indicating that fatty acids regulate PC expression and carbon flux, but that fatty acid flux control points are not connected to PC, PCK1, or PCK2. In conclusion, fatty acids regulate hepatic expression of PC, PCK1, and PCK2, and carbon flux, but the point of control is distinct.

Current Insights into the Effects of Dietary α-Linolenic Acid Focusing on Alterations of Polyunsaturated Fatty Acid Profiles in Metabolic Syndrome

The plant-derived α-linolenic acid (ALA) is an essential n-3 acid highly susceptible to oxidation, present in oils of flaxseeds, walnuts, canola, perilla, soy, and chia. After ingestion, it can be incorporated in to body lipid pools (particularly triglycerides and phospholipid membranes), and then endogenously metabolized through desaturation, elongation, and peroxisome oxidation to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), with a very limited efficiency (particularly for DHA), beta-oxidized as an energy source, or directly metabolized to C18-oxilipins. At this moment, data in the literature about the effects of ALA supplementation on metabolic syndrome (MetS) in humans are inconsistent, indicating no effects or some positive effects on all MetS components (abdominal obesity, dyslipidemia, impaired insulin sensitivity and glucoregulation, blood pressure, and liver steatosis). The major effects of ALA on MetS seem to be through its conversion to more potent EPA and DHA, the impact on the n-3/n-6 ratio, and the consecutive effects on the formation of oxylipins and endocannabinoids, inflammation, insulin sensitivity, and insulin secretion, as well as adipocyte and hepatocytes function. It is important to distinguish the direct effects of ALA from the effects of EPA and DHA metabolites. This review summarizes the most recent findings on this topic and discusses the possible mechanisms.

Circulating oxylipin and bile acid profiles of dexmedetomidine, propofol, sevoflurane, and S-ketamine: a randomised controlled trial using tandem mass spectrometry

Background

This exploratory study aimed to investigate whether dexmedetomidine, propofol, sevoflurane, and S-ketamine affect oxylipins and bile acids, which are functionally diverse molecules with possible connections to cellular bioenergetics, immune modulation, and organ protection.

Methods

In this randomised, open-label, controlled, parallel group, Phase IV clinical drug trial, healthy male subjects (n=160) received equipotent doses (EC50 for verbal command) of dexmedetomidine (1.5 ng ml-1; n=40), propofol (1.7 μg ml-1; n=40), sevoflurane (0.9% end-tidal; n=40), S-ketamine (0.75 μg ml-1; n=20), or placebo (n=20). Blood samples for tandem mass spectrometry were obtained at baseline, after study drug administration at 60 and 130 min from baseline; 40 metabolites were analysed.

Results

Statistically significant changes vs placebo were observed in 62.5%, 12.5%, 5.0%, and 2.5% of analytes in dexmedetomidine, propofol, sevoflurane, and S-ketamine groups, respectively. Data are presented as standard deviation score, 95% confidence interval, and P-value. Dexmedetomidine induced wide-ranging decreases in oxylipins and bile acids. Amongst others, 9,10-dihydroxyoctadecenoic acid (DiHOME) -1.19 (-1.6; -0.78), P<0.001 and 12,13-DiHOME -1.22 (-1.66; -0.77), P<0.001 were affected. Propofol elevated 9,10-DiHOME 2.29 (1.62; 2.96), P<0.001 and 12,13-DiHOME 2.13 (1.42; 2.84), P<0.001. Analytes were mostly unaffected by S-ketamine. Sevoflurane decreased tauroursodeoxycholic acid (TUDCA) -2.7 (-3.84; -1.55), P=0.015.

Conclusions

Dexmedetomidine-induced oxylipin alterations may be connected to pathways associated with organ protection. In contrast to dexmedetomidine, propofol emulsion elevated DiHOMEs, oxylipins associated with acute respiratory distress syndrome, and mitochondrial dysfunction in high concentrations. Further research is needed to establish the behaviour of DIHOMEs during prolonged propofol/dexmedetomidine infusions and to verify the sevoflurane-induced reduction in TUDCA, a suggested neuroprotective agent.

Clinical trial registration

NCT02624401.

Chiral 4-O-acylterpineol as transdermal permeation enhancers: insights of the enhancement mechanisms of a transdermal enantioselective delivery system for flurbiprofen

In order to devise more effective penetration enhancers, 4-O-acylterpineol derivatives which were expected to be hydrolyzed into nontoxic metabolites by esterase in the living epidermis, were synthesized from 4-terpineol (4-TER) enantiomers and straight chain fatty acids. Their promoting activities on the SR-flurbiprofen and its enantiomers were tested across full-thickness rabbit skin, as well as to correlate under in vitro and in vivo conditions. The permeation studies indicated that both d-4-O-acylterpineol and l-4-O-acylterpineol had significant enhancing effects, interestingly, d-4-O-aclyterpineol had higher enhancing effects than l-4-O-aclyterpineol with the exception of d-4-methyl-1-(1-methylethyl)-3-cyclohexen-1-yl octadec-9-enoate (d-4-T-dC18). The mechanism of 4-O-acylterpineol facilitating the drug penetration across the skin was confirmed by Attenuated total reflection-Fourier transformed infrared spectroscopy (ATR-FTIR) and molecular simulation. The mechanism of penetration enhancers promoting drug release was explored by the in vitro release experiment. Finally, a relative safety skin irritation of enhancers was also investigated by in vivo histological evaluation. The present research suggested that d-4-O-aclyterpineol and l-4-O-aclyterpineol could significantly promote the penetration of SR-flurbiprofen and its enantiomers both in vitro and in vivo, with the superiorities of high flux and low dermal toxicity.

A Combination of Flaxseed Oil and Astaxanthin Improves Hepatic Lipid Accumulation and Reduces Oxidative Stress in High Fat-Diet Fed Rats

Hepatic lipid accumulation and oxidative stress are crucial pathophysiological mechanisms for non-alcoholic fatty liver disease (NAFLD). Thus, we examined the effect of a combination of flaxseed oil (FO) and astaxanthin (ASX) on hepatic lipid accumulation and oxidative stress in rats fed a high-fat diet. ASX was dissolved in flaxseed oil (1 g/kg; FO + ASX). Animals were fed diets containing 20% fat, where the source was lard, or 75% lard and 25% FO + ASX, or 50% lard and 50% FO + ASX, or FO + ASX, for 10 weeks. Substitution of lard with FO + ASX reduced steatosis and reduced hepatic triacylglycerol and cholesterol. The combination of FO and ASX significantly decreased hepatic sterol regulatory element-binding transcription factor 1 and 3-hydroxy-3-methylglutaryl-CoA reductase but increased peroxisome proliferator activated receptor expression. FO + ASX significantly suppressed fatty acid synthase and acetyl CoA carboxylase but induced carnitine palmitoyl transferase-1 and acyl CoA oxidase expression. FO + ASX also significantly elevated hepatic SOD, CAT and GPx activity and GSH, and markedly reduced hepatic lipid peroxidation. Thus, FO and ASX may reduce NAFLD by reversing hepatic steatosis and reducing lipid accumulation and oxidative stress.

LA and ALA prevent glucose intolerance in obese male rats without reducing reactive lipid content, but cause tissue-specific changes in fatty acid composition

While the cause of Type 2 diabetes remains poorly defined, the accumulation of reactive lipids within white adipose tissue, skeletal muscle, and liver have been repeatedly implicated as underlying mechanisms. The ability of polyunsaturated fatty acids (PUFAs) to prevent the development of insulin resistance has gained considerable interest in recent years; however, the mechanisms-of-action remain poorly described. Therefore, we determined the efficacy of diets supplemented with either linoleic acid (LA) or α-linolenic acid (ALA) in preventing insulin resistance and reactive lipid accumulation in key metabolic tissues of the obese Zucker rat. Obese Zucker rats displayed impaired glucose homeostasis and reduced n-3 and n-6 PUFA content in the liver and epididymal white adipose tissue (EWAT). After the 12-wk feeding intervention, both LA- and ALA-supplemented diets prevented whole body glucose and insulin intolerance; however, ALA had a more pronounced effect. These changes occurred in association with n-3 and n-6 accumulation in all tissues studied, albeit to different extents (EWAT > liver > muscle). Triacylglycerol (TAG), diacylglycerol (DAG), ceramide, and sphingolipid accumulation were not attenuated in obese animals supplemented with either LA or ALA, suggesting that preservation of glucose homeostasis occurred independent of changes in reactive lipid content. However, PUFA-supplemented diets differentially altered the fatty acid composition of TAGs, DAGs, and PLs in a tissue-specific manner, suggesting essential fatty acid metabolism differs between tissues. Together, our results indicate that remodeling of the fatty acid composition of various lipid fractions may contribute to the improved glucose tolerance observed in obese rats fed PUFA-supplemented diets.

No positive influence of ingesting chia seed oil on human running performance

Runners (n = 24) reported to the laboratory in an overnight fasted state at 8:00 am on two occasions separated by at least two weeks. After providing a blood sample at 8:00 am, subjects ingested 0.5 liters flavored water alone or 0.5 liters water with 7 kcal kg⁻¹ chia seed oil (random order), provided another blood sample at 8:30 am, and then started running to exhaustion (~70% VO_2max). Additional blood samples were collected immediately post- and 1-h post-exercise. Despite elevations in plasma alpha-linolenic acid (ALA) during the chia seed oil (337%) versus water trial (35%) (70.8 ± 8.6, 20.3 ± 1.8 μg mL⁻¹, respectively, p < 0.001), run time to exhaustion did not differ between trials (1.86 ± 0.10, 1.91 ± 0.13 h, p = 0.577, respectively). No trial differences were found for respiratory exchange ratio (RER) (0.92 ± 0.01), oxygen consumption, ventilation, ratings of perceived exertion (RPE), and plasma glucose and blood lactate. Significant post-run increases were measured for total leukocyte counts, plasma cortisol, and plasma cytokines (Interleukin-6 (IL-6), Interleukin-8 (IL-8), Interleukin-10 (IL-10), and Tumor necrosis factors-α (TNF-α)), with no trial differences. Chia seed oil supplementation compared to water alone in overnight fasted runners before and during prolonged, intensive running caused an elevation in plasma ALA, but did not enhance run time to exhaustion, alter RER, or counter elevations in cortisol and inflammatory outcome measures.

Lipid metabolic dose response to dietary alpha-linolenic acid in monk parrot (Myiopsitta monachus)

Monk parrots (Myiopsitta monachus) are susceptible to atherosclerosis, a progressive disease characterized by the formation of plaques in the arteries accompanied by underlying chronic inflammation. The family of n-3 fatty acids, especially eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), have consistently been shown to reduce atherosclerotic risk factors in humans and other mammals. Some avian species have been observed to convert α-linolenic acid (18:3n-3, ALA) to EPA and DHA (Htin et al. in Arch Geflugelk 71:258-266, 2007; Petzinger et al. in J Anim Physiol Anim Nutr, 2013). Therefore, the metabolic effects of including flaxseed oil, as a source of ALA, in the diet at three different levels (low, medium, and high) on the lipid metabolism of Monk parrots was evaluated through measuring plasma total cholesterol (TC), free cholesterol (FC), triacylglycerols (TAG), and phospholipid fatty acids. Feed intake, body weight, and body condition score were also assessed. Thus the dose and possible saturation response of increasing dietary ALA at constant linoleic acid (18:2n-6, LNA) concentration on lipid metabolism in Monk parrots (M. monachus) was evaluated. Calculated esterified cholesterol in addition to plasma TC, FC, and TAG were unaltered by increasing dietary ALA. The high ALA group had elevated levels of plasma phospholipid ALA, EPA, and docosapentaenoic acid (DPAn-3, 22:5n-3). The medium and high ALA groups had suppressed plasma phospholipid 20:2n-6 and adrenic acid (22:4n-6, ADA) compared to the low ALA group. When the present data were combined with data from a previous study (Petzinger et al. in J Anim Physiol Anim Nutr, 2013) a dose response to dietary ALA was observed when LNA was constant. Plasma phospholipid ALA, EPA, DPAn-3, DHA, and total n-3 were positively correlated while 20:2n-6, di-homo-gamma-linoleic acid (20:3n-6Δ7), arachidonic acid (20:4n-6), ADA, and total n-6 were inversely correlated with dietary en% ALA.

Postprandial effects of a lipid-rich meal in the rat are modulated by the degree of unsaturation of 18C fatty acids

The fatty acid composition of high-fat diets is known to influence the magnitude of postprandial events that increase the risk of metabolic syndrome. These variations in magnitude may be directly ascribed to differences in the channeling of lipids toward oxidation or storage. A study was designed to compare the effects of 4 dietary fats on postprandial energy expenditure and on some risk factors of the metabolic syndrome. To avoid usual confounding factors due to simultaneous variations in chain length and double-bounds number of fatty acids, dietary fats were chosen to provide mainly 18-carbon fatty acids with 0 (stearic acid [SA]), 1 (oleic acid [OA]), 2 (linoleic acid [LA]), or 3 (alpha-linolenic acid [ALA]) double bounds. They were given as single high-fat test meals to 4 different groups of male rats. The resting metabolic rate and the lipid and carbohydrate oxidation were measured from oxygen consumption and carbon dioxide production using indirect calorimetry 2 hours before and 6.5 hours after the test meal. Plasma glucose, triglyceride, and chylomicron concentrations were determined at 0, 1.5, and 4 hours after the test meal. Postprandial concentration of glucose and triglyceride did not vary with the nature of the test meals, whereas that of chylomicrons was the highest after the LA test meal and the lowest after the SA test meal. Postprandial increase in resting metabolic rate was the highest after the LA and OA test meals, and the lowest after the SA and ALA test meals. Compared with the 3 other diets, the ALA test meal enhanced lipid oxidation and decreased glucose oxidation during the early postprandial period (0.25-3.25 hours). This suggests that stearic acid may not induce all the adverse effects classically described for other saturated fatty acids and that alpha-linolenic acid may beneficially influence energy partitioning, especially during the early postprandial state.

Hypolipidaemic effects of fenofibrate and fasting in the herbivorous grass carp ( Ctenopharyngodon idella) fed a high-fat diet

We investigated whether the hypolipidaemic effect of fenofibrate and fasting observed in most omnivorous mammals may also apply to herbivorous fish. Grass carp (Ctenopharyngodon idella) fed a high-fat (8 %) diet exhibited a marked increase in blood lipids and body fat after 6 weeks. They were then treated with fenofibrate (100 mg/kg body weight) in the same high-fat diet for 2 weeks, followed by fasting for 1 week. Plasma lipid concentration, body fat amount, fatty acid composition, plasma thiobarbituric acid-reactive substances and some parameters related to hepatic fatty acid oxidation were measured, and liver samples were stained for histological examination. Fenofibrate treatment decreased TAG and cholesterol concentrations in plasma, total lipids of the whole body and liver, and EPA and DHA contents in tissues. Further, a mobilisation of mesenteric fat concomitant with an increase in hepatic peroxisomal fatty acid oxidation and lipid peroxidation was observed. Compared with fenofibrate treatment, fasting decreased body weight and plasma TAG, but not plasma cholesterol. It also reduced the fat content of the whole body and increased the EPA and DHA contents in the liver and other tissues. Fatty acid oxidation was stimulated by fasting in mitochondria, but not in peroxisomes. These data suggest that fenofibrate and fasting regulate the lipid metabolism in grass carp through different metabolic pathways. The grass carp is moderately responsive to a fibrate derivative in comparison with the well-known excess responsiveness of the rat model, and so it could be used for the study of lipid abnormalities as a herbivorous model.

Dietary α-linolenic acid and health-related outcomes: a metabolic perspective

α-Linolenic acid (αLNA; 18: 3n-3) is essential in the human diet, probably because it is the substrate for the synthesis of longer-chain, more unsaturatedn-3 fatty acids, principally EPA (20: 5n-3) and DHA (22: 6n-3), which confer important biophysical properties on cell membranes and so are required for tissue function. The extent to which this molecular transformation occurs in man is controversial. The present paper reviews the recent literature on the metabolism of αLNA in man, including the use of dietary αLNA in β-oxidation, recycling of carbon by fatty acid synthesisde novoand conversion to longer-chain PUFA. Sex differences in αLNA metabolism and the possible biological consequences are discussed. Increased consumption of EPA and DHA in fish oil has a number of well-characterised beneficial effects on health. The present paper also reviews the efficacy of increased αLNA consumption in increasing the concentrations of EPA and DHA in blood and cell lipid pools, and the extent to which such dietary interventions might be protective against CVD and inflammation. Although the effects on CVD risk factors and inflammatory markers are variable, where beneficial effects have been reported these are weaker than have been achieved from increasing consumption of EPA+DHA or linoleic acid. Overall, the limited capacity for conversion to longer-chainn-3 fatty acids, and the lack of efficacy in ameliorating CVD risk factors and inflammatory markers in man suggests that increased consumption of αLNA may be of little benefit in altering EPA+DHA status or in improving health outcomes compared with other dietary interventions.

Hepatic Lipid Metabolism in Transition Dairy Cows Fed Flaxseed

Thirty-three Holstein cows averaging 687 kg of body weight were allotted 6 wk before the expected date of parturition to 11 groups of 3 cows blocked within parity for similar calving dates to determine the effects of feeding different sources of fatty acids on blood parameters related to fatty liver and profile of fatty acids in plasma and liver. Cows were fed lipid supplements from 6 wk before the expected date of parturition until d 28 of lactation. Cows within each block were assigned to 1 of 3 isonitrogenous and isoenergetic dietary supplements: control with no added lipids (CO); unsaturated lipids supplied as whole flaxseed (FL; 3.3 and 11.0% of the dry matter in prepartum and postpartum diets, respectively); and saturated lipids supplied as Energy Booster (EB; 1.7 and 3.5% of the DM in prepartum and postpartum diets, respectively). Diets EB and FL had similar ether extract concentrations. Multiparous cows fed EB had lower dry matter intake and milk production, higher concentrations of nonesterified fatty acids and beta-hydroxybutyrate in plasma and triglycerides (TG) and total lipids in liver, and lower concentrations of plasma glucose and liver glycogen than those fed FL and CO. Production of 4% fat-corrected milk was similar among treatments. Multiparous cows fed FL had the highest liver concentrations of glycogen on wk 2 and 4 after calving and lowest concentrations of TG on wk 4 after calving. Liver C16:0 relative percentages in multiparous cows increased after calving whereas those of C18:0 decreased. Relative percentages of liver C16:0 were higher in wk 2 and 4 postpartum for multiparous cows fed EB compared with those fed CO and FL; those of C18:0 were lower in wk 4 postpartum for cows fed EB compared with those fed CO and FL. Liver C18:1 relative percentages of multiparous cows increased after calving and were higher in wk 4 for cows fed EB compared with those fed CO and FL. The inverse was observed for liver C18:2 relative percentages. In general, diets had more significant effects on plasma concentrations of nonesterified fatty acids, beta-hydroxybutyrate, and glucose and liver profiles of fatty acids, TG, total lipids, and glycogen of multiparous than primiparous cows. These data suggest that feeding a source of saturated fatty acids increased the risk of fatty liver in the transition cow compared with feeding no lipids or whole flaxseed. Feeding flaxseed compared with no lipids or a source of saturated fatty acids from 6 wk before calving could be a useful strategy to increase liver concentrations of glycogen and decrease liver concentrations of TG after calving, which may prevent the development of fatty liver in the transition dairy cow.

Decreasing linoleic acid with constant alpha-linolenic acid in dietary fats increases (n-3) eicosapentaenoic acid in plasma phospholipids in healthy men

High linoleic acid (LA) intakes have been suggested to reduce alpha-linolenic acid [ALA, 18:3(n-3)] metabolism to eicosapentaenoic acid [EPA, 20:5(n-3)] and docosahexaenoic acid [DHA, 22:6(n-3)], and favor high arachidonic acid [ARA, 20:4(n-6)]. We used a randomized cross-over study with men (n = 22) to compare the effect of replacing vegetable oils high in LA with oils low in LA in foods, while maintaining constant ALA, for 4 wk each, on plasma (n-3) fatty acids. Nonvegetable sources of fat, except fish and seafoods, were unrestricted. We determined plasma phospholipid fatty acids at wk 0, 2, 4, 6, and 8, and triglycerides, cholesterol, serum CRP, and IL-6, and platelet aggregation at wk 0, 4, and 8. LA and ALA intakes were 3.8 +/- 0.12% and 1.0 +/- 0.05%, and 10.5 +/- 0.53% and 1.1 +/- 0.06% energy with LA:ALA ratios of 4:0 and 10:1 during the low and high LA diets, respectively. The plasma phospholipid LA was higher and EPA was lower during the high than during the low LA diet period (P < 0.001), but DHA declined over the 8-wk period (r = -0.425, P < 0.001). The plasma phospholipid ARA:EPA ratios were (mean +/- SEM) 20.7 +/- 1.52 and 12.9 +/- 1.01 after 4 wk consuming the high or low LA diets, respectively (P < 0.001); LA was inversely associated with EPA (r = -0.729, P < 0.001) but positively associated with ARA:EPA (r = 0.432, P < 0.001). LA intake did not influence ALA, ARA, DPA, DHA, or total, LDL or HDL cholesterol, CRP or IL-6, or platelet aggregation. In conclusion, high LA intakes decrease plasma phospholipid EPA and increase the ARA:EPA ratio, but do not favor higher ARA.

High Doses of Stavudine Induce Fat Wasting and Mild Liver Damage without Impairing Mitochondrial Respiration in Mice

Objective

Stavudine (d4T), a nucleoside reverse-transcriptase inhibitor (NRTI), can induce lipoatrophy, fatty liver, hyperlactataemia and abnormal liver tests. NRTI toxicity is usually ascribed to mitochondrial DNA (mtDNA) depletion and impaired mitochondrial respiration. However, NRTIs could have effects unrelated to mtDNA. Recently, we reported that 100 mg/kg/day of d4T stimulated fatty acid oxidation (FAO) in mouse liver, and reduced body fatness without depleting white adipose tissue (WAT) mtDNA. We hypothesized that higher d4T doses could further reduce adiposity, while inhibiting hepatic FAO.

Methods

Mice were treated for 2 weeks with d4T (500 mg/kg/day), L-carnitine (200 mg/kg/day) or both drugs concomitantly. Body fatness was assessed by dual energy X-ray absorptiometry, and investigations were performed in plasma, liver, muscle and WAT.

Results

D4T reduced the gain of body adiposity, WAT leptin, whole body FAO and plasma ketone bodies, and increased liver triglycerides and plasma aminotransferases with mild ultrastructural abnormalities in hepatocytes. Plasma lactate and respiratory chain activities in tissues were unchanged. Stearoyl-CoA desaturase (SCD-1), an enzyme negatively regulated by leptin, was overexpressed in liver. High doses of β-aminoisobutyric acid (BAIBA), a d4T catabolite, increased plasma ketone bodies. Although L-carnitine did not correct body adiposity, it prevented d4T-induced impairment of FAO and liver abnormalities.

Conclusions

D4T overdosage triggers fat wasting, leptin insufficiency and mild liver damage, without causing respiratory chain dysfunction. Overexpression of SCD-1 reduces fatty acid oxidation and overcomes the stimulating effect of BAIBA on hepatic FAO. L-carnitine does not correct leptin insufficiency but prevents d4T-induced impairment of FAO and liver damage.

Biochemical hepatic alterations and body lipid composition in the herbivorous grass carp (Ctenopharyngodon idella) fed high-fat diets

High-fat diets may have favourable effects on growth of some carnivorous fish because of the protein-sparing effect of lipids, but high-fat diets also exert some negative impacts on flesh quality. The goal of the study was therefore to determine the effects of fat-enriched diets in juvenile grass carp (Ctenopharyngodon idella) as a typical herbivorous fish on growth and possible lipid metabolism alterations. Three isonitrogenous diets containing 2, 6 or 10% of a mixture of lard, maize oil and fish oil (1:1:1, by weight) were applied to fish for 8 weeks in a recirculation system. Data show that feeding diets with increasing lipid levels resulted in lowered feed intake, decreased growth and feed efficiency, and increased mesenteric fat tissue weight. Concomitantly, alteration of lipoprotein synthesis and greater level of lipid peroxidation were apparent in blood. In liver, muscle and mesenteric fat tissue, the percentages of α-linolenic acid and DHA were significantly increased or tended to increase with higher dietary lipid levels. Biochemical activity measurements performed on liver showed that, with the increase in dietary lipid level, there was a decrease in both mitochondrial and peroxisomal fatty acid oxidation capacities, which might contribute, at least in part, to the specific accumulation of α-linolenic acid and DHA into cells more active in membrane building. On the whole, grass carp have difficulty in energetically utilising excess dietary fat, especially when enriched in n−3 PUFA that are susceptible to peroxidation.

Metabolism of alpha-linolenic acid in humans

Alpha-linolenic acid (18:3n-3) is essential in the human diet, probably because it is the substrate for the synthesis of longer-chain, more unsaturated n-3 fatty acids eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) which are required for tissue function. This article reviews the recent literature on 18:3n-3 metabolism in humans, including fatty acid beta-oxidation, recycling of carbon by fatty acid synthesis de novo and conversion to longer-chain polyunsaturated fatty acids (PUFA). In men, stable isotope tracer studies and studies in which volunteers increased their consumption of 18:3n-3 show conversion to 20:5n-3 and 22:5n-3, but limited conversion to 22:6n-3. However, conversion to 18:3n-3 to 20:5n-3 and 22:6n-3 is greater in women compared to men, due possibly to a regulatory effect of oestrogen, while partitioning of 18:3n-3 towards beta-oxidation and carbon recycling was lower than in men. These gender differences may be an important consideration in making dietary recommendations for n-3 PUFA intake.

Alteration of 20:5n-3 and 22:6n-3 fat contents and liver peroxisomal activities in fenofibrate-treated rainbow trout

Fish easily accumulate n-3 PUFA of exogenous origin, but the underlying mechanisms are not well established in the whole animal. This study was undertaken to investigate whether this feature was physiologically associated with mitochondrial and peroxisomal capacities that differentially affect FA oxidation. For this purpose, peroxisomal FA oxidation was increased by treating rainbow trout with fenofibrate, which strongly stimulates the peroxisome proliferator-activated receptor-a in rodents. Diets containing EPA and DHA, with or without fenofibrate added, were administered to male trout for 12 d. After treatment, neither liver hypertrophy nor accumulation of fat was apparent within the liver and muscle cells. However, fenofibrate treatment decreased the contents of EPA and DHA in the liver, white muscle, and intraperitoneal fat tissue, which represented (per whole body) at least 280 mg less than in controls. Carnitine-dependent palmitate oxidation rates, expressed per gram of liver, were slightly increased by fenofibrate when measured from tissue homogenates and were unchanged when calculated from isolated mitochondria, relative to control fish. The treatment altered neither carnitine palmitoyltransferase I activity rates, expressed per gram of liver, nor the sensitivity of the enzyme to malonyl-CoA inhibition, but did increase the malonyl-CoA content (+45%). Meanwhile, fenofibrate increased (by about 30%) the peroxisome-related activities, i.e., catalase, carnitine-independent palmitate oxidation, acyl-CoA oxidase, and the peroxisomal FA-oxidizing system, relative to the control group. The data strongly suggest that the induction of peroxisomal activities, some of which being able to oxidize very long chain FA, was responsible for the lower contents of EPA and DHA in the body lipids of fenofibrate-treated trout.

Metabolism of polyunsaturated fatty acids and ketogenesis: an emerging connection

This paper summarizes the emerging literature indicating that at least two polyunsaturated fatty acids (PUFA; linoleate, alpha-linolenate) are moderately ketogenic and that via ketone bodies significant amounts of carbon are recycled from these fatty acids into de novo synthesis of lipids including cholesterol, palmitate, stearate and oleate. This pathway (PUFA carbon recycling) is particularly active in several tissues during the suckling period when, depending on the tissue, >200 fold more carbon from alpha-linolenate can be recycled into newly synthesized lipids than is used to make docosahexaenoate. At least in rats, PUFA carbon recycling also occurs in adults and even during extreme linoleate deficiency. Hence, this pathway should be considered an obligatory component of PUFA metabolism. It is still speculative but part of the clinical benefit of the very high fat ketogenic diet in intractable seizures may be achieved by raising plasma levels of PUFA that have anti-seizure effects, especially arachidonate and docosahexaenoate. Hence, in addition to some PUFA being ketogenic substrates, the state of ketosis involves potentially beneficial changes in PUFA homeostasis. Both the molecular controls on these pathways and their clinical significance still need elucidation.

Problems with essential fatty acids: time for a new paradigm?

The term 'essential fatty acid' is ambiguous and inappropriately inclusive or exclusive of many polyunsaturated fatty acids. When applied most rigidly to linoleate and alpha-linolenate, this term excludes the now well accepted but conditional dietary need for two long chain polyunsaturates (arachidonate and docosahexaenoate) during infancy. In addition, because of the concomitant absence of dietary alpha-linolenate, essential fatty acid deficiency is a seriously flawed model that has probably led to significantly overestimating linoleate requirements. Linoleate and alpha-linolenate are more rapidly beta-oxidized and less easily replaced in tissue lipids than the common 'non-essential' fatty acids (palmitate, stearate, oleate). Carbon from linoleate and alpha-linolenate is recycled into palmitate and cholesterol in amounts frequently exceeding that used to make long chain polyunsaturates. These observations represent several problems with the concept of 'essential fatty acid', a term that connotes a more protected and important fatty acid than those which can be made endogenously. The metabolism of essential and non-essential fatty acids is clearly much more interconnected than previously understood. Replacing the term 'essential fatty acid' by existing but less biased terminology, i.e. polyunsaturates, omega3 or omega6 polyunsaturates, or naming the individual fatty acid(s) in question, would improve clarity and would potentially promote broader exploration of the functional and health attributes of polyunsaturated fatty acids.

Cholesterol synthesis in mice is suppressed but lipofuscin formation is not affected by long-term feeding of n-3 fatty acid-enriched oils compared with lard and n-6 fatty acid-enriched oils

Hypocholesterolemic activity of dietary polyunsaturated fatty acids is observed after relatively short-term but not long-term feedings, and their long-term feedings are suspected to accelerate aging through tissue accumulation of lipid peroxides and age pigments (lipofuscin). To define the long-term effects of fats and oils in more detail, female mice were fed a conventional basal diet supplemented with lard (Lar), high-linoleic (n-6) safflower oil (Saf), rapeseed oil (Rap), high-alpha-linolenic (n-3) perilla oil (Per), or a mixture of ethyl docosahexaenoate and soybean oil (DHA/Soy) from 17 weeks to 71 weeks of age. The DHA/Soy and Per groups had decreased serum cholesterol levels compared with the Lar and Saf groups, but the difference between the Lar and Saf groups was not significant. The 3-hydroxy-3-methyglutary-CoA (HMG-CoA) reductase activity in the liver was also significantly lower in the Per and DHA/Soy groups. However, no significant difference in lipofuscin contents in the brain and liver was observed among the 5 dietary groups, despite significant differences in peroxidizability indices of the dietary and/or tissue lipids. These results indicate that n-3 fatty acid-rich oils are hypocholesterolemic by suppressing hepatic HMG-CoA reductase activity compared with animal fats and high-linoleic (n-6) oil, but tissue lipofuscin contents are not affected by a long-term feeding of fats and oils with different degree of unsaturation in mice.

Why is carbon from some polyunsaturates extensively recycled into lipid synthesis?

We summarize here the evidence indicating that carbon from alpha-linolenate and linoleate is readily recycled into newly synthesized lipids. This pathway consumes the majority of these fatty acids that is not beta-oxidized as a fuel. Docosahexaenoate undergoes less beta-oxidation and carbon recycling than do alpha-linolenate or linoleate, but is it still actively metabolized by this pathway? Among polyunsaturates, arachidonate appears to undergo the least beta-oxidation and carbon recycling, an observation that may help account for the resistance of brain membranes to loss of arachidonate during dietary deficiency of n-6 polyunsaturates. Preliminary evidence suggests that de novo lipid synthesis consumes carbon from alpha-linolenate and linoleate in preference to palmitate, but this merits systematic study. Active beta-oxidation and carbon recycling of 18-carbon polyunsaturates does not diminish the importance of being able to convert alpha-linolenate and linoleate to long-chain polyunsaturates but suggests that a broad perspective is required in studying the metabolism of polyunsaturates in general and alpha-linolenate and linoleate in particular.

The role of carnitine in normal and altered fatty acid metabolism

Carnitine is a low-molecular-weight compound obtained from the diet that also is biosynthesized from the essential amino acids lysine and methionine. Carnitine has been identified in a variety of mammalian tissues and has an obligate role in the mitochondrial oxidation of long-chain fatty acids through the action of specialized acyltransferases. Other roles for carnitine include buffering of the acyl coenzyme A (CoA)-CoA ratio, branched-chain amino acid metabolism, removal of excess acyl groups, and peroxisomal fatty acid oxidation. The growing body of evidence about carnitine function has led to increased understanding and identification of disorders associated with altered carnitine metabolism. Disorders of fatty acid oxidation and metabolism typically are associated with primary and secondary forms of carnitine deficiency. These disorders, which include increased lipolysis, increased lipid peroxidation, accumulation of acylcarnitines, and altered membrane permeability, have significant consequences for patients with myocardial diseases and kidney failure. Therapeutic administration of carnitine shows promise in treating selected groups of patients who have altered carnitine homeostasis, resulting in improved cardiac function, increased exercise capacity, reduced muscle cramps, and reduced intradialytic complications.

Conjugated linoleic acid isomers in mitochondria: evidence for an alteration of fatty acid oxidation

The beneficial effects exerted by low amounts of conjugated linoleic acids (CLA) suggest that CLA are maximally conserved and raise the question about their mitochondrial oxidizability. Cis-9,trans-11-C(18:2) (CLA1) and trans-10,cis-12-C(18:2) (CLA2) were compared to cis-9,cis-12-C(18:2) (linoleic acid; LA) and cis-9-C(16:1) (palmitoleic acid; PA), as substrates for total fatty acid (FA) oxidation and for the enzymatic steps required for the entry of FA into rat liver mitochondria. Oxygen consumption rate was lowest when CLA1 was used as a substrate with that on CLA2 being intermediate between it and the respiration on LA and PA. The order of the radiolabeled FA oxidation rate was PA >> LA > CLA2 > CLA1. Transesterification to acylcarnitines of the octadecadienoic acids were similar, while uptake across inner membranes of CLA1 and, to a lesser extent, of CLA2 was greater than that of LA or PA. Prior oxidation of CLA1 or CLA2 made re-isolated mitochondria much less capable of oxidising PA or LA under carnitine-dependent conditions, but without altering the carnitine-independent oxidation of octanoic acid. Therefore, the CLA studied appeared to be both poorly oxidizable and capable of interfering with the oxidation of usual FA at a step close to the beginning of the beta-oxidative cycle.

Docosahexaenoic acid and arachidonic acid in infant development

Docosahaxaenoic acid and arachidonic acid are highly concentrated in the central nervous system. The amount of these fatty acids in the central nervous system increases dramatically during the last intrauterine trimester and the first year of life. A central question of research conducted during the past 20 years is if the essential fatty acid precursor of docosahexaenoic acid is sufficient to achieve optimal DHA accumulation in the central nervous system and, therefore, infant development. The important role of non-human primate studies in characterising the behavioral effects of n-3 essential fatty acid deficiency and subsequent low brain DHA accumulation, the difference between essential fatty acid deficiencies and conditional deficiencies of docosahexaenoic acid and arachidonic acid, and the evidence that human infants have a conditionally essential need for docosahexaenoic acid and, perhaps, for arachidonic acid are summarised. The current suggestive evidence for several possible mechanisms underlying behavioral effects are also provided.

Effect of dietary oils enriched with n-3 fatty acids on survival of mice

Female mice were fed a conventional diet, shifted at 119 days of age to a diet supplemented with 10 wt % lard (Lar), high-linoleic (n-6) safflower oil (Saf), rapeseed oil (low-erucic, Rap), high-alpha-linolenic (n-3) perilla oil (Per) or a mixture (1:9) of ethyl docosahexaenoate (n-3) and soybean oil (DHA/Soy). Weight gain was less in the Per group than in the other groups at 497 days of age. In the Rap group, proteinuria was more severe than in the Saf, Per and DHA/Soy group, and hepatic triacylglycerol accumulation was greater than in the other groups. The mean survival time of the DHA/Soy group (753 days) was significantly longer than in the Lar group (672 days) and Saf group (689 days); the differences among other groups (e.g., 701 days in the Per group and 712 days in the Rap group) were not statistically significant. Although DHA is more susceptible to auto-oxidation than other major fatty acids in the air, an oil containing DHA was found to increase the survival of mice. Rapeseed oil that decreases the survival time of SHRSP rats was found to be safe in the mouse strain used in this study when survival was an end point.

Cyclic fatty acid monomers from heated oil modify the activities of lipid synthesizing and oxidizing enzymes in rat liver

Cyclic fatty acid monomers purified from a heated linseed oil were given for 2 wk to adult rats as triacylglycerol at two dose levels, i.e., 0.1 and 1 g/100 g diet, to determine their effect on some aspects of lipid metabolism. Indirect evidence of a peroxisome proliferator-like effect was observed, as determined by an elevation of some characteristic enzyme activities, such as peroxisomal acyl-CoA oxidase, and the microsomal omega- but also (omega-1)-laurate hydroxylase (CYP4A1 and CYP2E1, respectively). The dietary cyclic fatty acids induced a coordinated regulation between the activities of the lipogenic enzymes studied (Delta9-desaturase, phosphatidate phosphohydrolase) and peroxisomal oxidation, but not with mitochondrial beta-oxidation. The dose-dependent decrease of Delta9-desaturase activity (P < 0.05) with cyclic fatty acid monomer intake was accompanied by a similar decrease of the monounsaturated fatty acid level in liver. The increase in the gamma-linolenic acid level also suggested an increase in Delta6-desaturase activity with cyclic fatty acid intake (P < 0.05). In addition, our results strongly suggested that the altered liver levels of eicosapentaenoic and arachidonic acids were due to the peroxisomal retroconversion process in rats fed cyclic acids. Finally, an effect of these cyclic compounds on the carbohydrate metabolism cannot be disregarded because they decreased liver glycogen concentration. We conclude that cyclic fatty acid monomers affect different aspects of lipid metabolism, including a phenotypic peroxisome proliferator response. This provides the ground for further studies investigating the biochemical pathways that underlie the nutritional effect of such molecules.

Comparative effects of perilla and fish oils on the activity and gene expression of fatty acid oxidation enzymes in rat liver

The activity and mRNA level of hepatic enzymes in fatty acid oxidation and synthesis were compared in rats fed diets containing either 15% saturated fat (palm oil), safflower oil rich in linoleic acid, perilla oil rich in alpha-linolenic acid or fish oil rich in eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) for 15 days. The mitochondrial fatty acid oxidation rate was 50% higher in rats fed perilla and fish oils than in the other groups. Perilla and fish oils compared to palm and safflower oils approximately doubled and more than tripled, respectively, peroxisomal fatty acid oxidation rate. Compared to palm and safflower oil, both perilla and fish oils caused a 50% increase in carnitine palmitoyltransferase I activity. Dietary fats rich in n-3 fatty acids also increased the activity of other fatty acid oxidation enzymes except for 3-hydroxyacyl-CoA dehydrogenase. The extent of the increase was greater with fish oil than with perilla oil. Interestingly, both perilla and fish oils decreased the activity of 3-hydroxyacyl-CoA dehydrogenase measured using short- and medium-chain substrates. Compared to palm and safflower oils, perilla and fish oils increased the mRNA level of many mitochondrial and peroxisomal enzymes. Increases were generally greater with fish oil than with perilla oil. Fatty acid synthase, glucose-6-phosphate dehydrogenase, and pyruvate kinase activity and mRNA level were higher in rats fed palm oil than in the other groups. Among rats fed polyunsaturated fats, activities and mRNA levels of these enzymes were lower in rats fed fish oil than in the animals fed perilla and safflower oils. The values were comparable between the latter two groups. Safflower and fish oils but not perilla oil, compared to palm oil, also decreased malic enzyme activity and mRNA level. Examination of the fatty acid composition of hepatic phospholipid indicated that dietary alpha-linolenic acid is effectively desaturated and elongated to form EPA and DHA. Dietary perilla oil and fish oil therefore exert similar physiological activity in modulating hepatic fatty acid oxidation, but these dietary fats considerably differ in affecting fatty acid synthesis.

Reciprocal enzymatic interference of carnitine palmitoyltransferase I and glycerol-3-phosphate acyltransferase in purified liver mitochondria

(i) Highly purified mitochondrial fractions were practically devoid of microsomal contamination and of acyl-CoA ligase activity. (ii) In mitochondria, glycerol-3-phosphate acyltransferase (GPAT) activity was supported by two enzymes, the first being very active at low palmitoyl-CoA/albumin ratios and sensitive to external agents (external form), the second being detected only at higher palmitoyl-CoA/albumin ratios and insensitive to external agents (internal form). (iii) Carnitine palmitoyltransferase I (CPT I) activity was shown to inhibit external GPAT activity only. (iv) Glycerol-3-phosphate exerted an inhibitory effect on CPT I, even when GPAT was inactive. Reciprocal interaction of CPT I and GPAT was discussed with regard to the balance existing between fatty acid oxidation and esterification metabolic pathways.

Hypolipidaemic effects of fenofibrate are not altered by mildronate-mediated normalization of carnitine concentration in rat liver

The five-fold higher carnitine content in the liver of fenofibrate-treated rats addresses the question about the possible role of this enhancement in the hypolipidaemic effect of the drug and the underlying mechanisms. When fenofibrate was administered with mildronate (a gamma-butyrobetaine hydroxylase inhibitor) in suitable amount, the content in carnitine was found to be normalized in liver. However, triglyceride contents of liver and serum were then at least as low as in rats treated by fenofibrate only. When carnitine concentration was lowered by mildronate to the third of the normal value, a marked increase in triglycerides occurred both in liver and serum, while the five-fold increase in carnitine due to fenofibrate enhanced blood ketone body concentration with no effect on liver and serum triglycerides. Data suggest that the normal carnitine concentration is largely sufficient to meet the usual requirement for carnitine palmitoyltransferase I activity (CPT I). In rat liver, increase in mitochondrial CPT I activity and in peroxisomal fatty acid oxidation may constitute part of the hypolipidaemic effect of fenofibrate.

Palmitate oxidation by the mitochondria from volume-overloaded rat hearts

In this work, an attempt was made to identify the reasons of impaired long-chain fatty acid utilization that was previously described in volume-overloaded rat hearts. The most significant data are the following: (1) The slowing down of long-chain fatty acid oxidation in severely hypertrophied hearts cannot be related to a feedback inhibition of carnitine palmitoyltransferase I from an excessive stimulation of glucose oxidation since, because of decreased tissue levels of L-carnitine, glucose oxidation also declines in volume-overloaded hearts. (2) While, in control hearts, the estimated intracellular concentrations of free carnitine are in the range of the respective Km of mitochondrial CPT I, a kinetic limitation of this enzyme could occur in hypertrophied hearts due to a 40% decrease in free carnitine. (3) The impaired palmitate oxidation persists upon the isolation of the mitochondria from these hearts even in presence of saturating concentrations of L-carnitine. In contrast, the rates of the conversion of both palmitoyl-CoA and palmitoylcarnitine into acetyl-CoA are unchanged. (4) The kinetic analyses of palmitoyl-CoA synthase and carnitine palmitoyltransferase I reactions do not reveal any differences between the two mitochondrial populations studied. On the other hand, the conversion of palmitate into palmitoylcarnitine proves to be substrate inhibited already at physiological concentrations of exogenous palmitate. The data presented in this work demonstrate that, during the development of severe cardiac hypertrophy, a fragilization of the mitochondrial outer membrane may occur. The functional integrity of this membrane seems to be further deteriorated by increasing concentrations of free fatty acids which gives rise to an impaired cooperation between palmitoyl-CoA synthase and carnitine palmitoyltransferase I. In intact myocardium, the utilization of the in situ generated palmitoyl-CoA can be further slowed down by decreased intracellular concentrations of free carnitine.

Effects of saturated and polyunsaturated fatty acids on human tumor-cell proliferation

1. Fatty acids of varying chain length and degree of unsaturation were found to inhibit the proliferation of T24/83, Hep2 and LLC-WRC256 tumor cell lines. 2. There was a strong correlation (r2= -0.956 to -0.995) between the degree of inhibition of proliferation and the degree of unsaturation of 18-carbon fatty acids for all the cell lines studied. No correlation existed in this respect for the 20-carbon fatty acids. 3. Tumor cells can differentiate between the degree of unsaturation of the 18-carbon fatty acids, and this ability is ultimately manifested in the rate of proliferation; however, the mechanisms remain to be identified.

Cellular uptake of stearic, oleic, linoleic, and linolenic acid and their effects on synthesis and secretion of lipids in Hep-G2 cells

The present study was undertaken to examine the cellular uptake of stearic (18:0), oleic (18:1), linoleic (18:2), and linolenic acid (18:3), and their effects on synthesis and secretion of lipids in Hep-G2 cells. The cells were grown for 6 days in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum. On day 7, cells were incubated in a serum-free DMEM containing 0.25-1.0 mM of 18:0, 18:1, 18:2 or 18:3. The cellular uptake of these fatty acids was almost linear during the 4 hr incubation period, and no significant differences were noted among the fatty acids tested, regardless of their degree of unsaturation. The treatment of cells with 1.0 mM of these fatty acids stimulated triglyceride (TG) synthesis nearly ten-fold and phospholipid (PL) synthesis approx, two-fold compared with those of the control. The lipoprotein-TG secretion also increased and was the highest with 18:1 followed in descending order by 18:2, 18:3, and 18:0. The fatty acid treatment of cells also significantly increased the incorporation of 14C-acetate into the cellular and lipoprotein cholesterol compared with that of the control (p < 0.05). In addition, notable changes occurred in the fatty acid composition of cellular and medium lipids, which were enriched with the particular fatty acid present in the incubation medium. The findings that 18:0, 18:1, 18:2, and 18:3 were taken up by Hep-G2 cells at almost identical rates demonstrate that differences in the cellular synthesis of lipids and their secretion are attributable to the metabolic specificity of those fatty acids, rather than variable rates of their uptake.

Effect of short- and long-term treatments by a low level of dietary L-carnitine on parameters related to fatty acid oxidation in Wistar rat

This study was designed to examine whether short- and long-term treatments by a low level of dietary L-carnitine are capable of altering enzyme activities related to fatty acid oxidation in normal Wistar rats. Under controlled feeding, ten days of treatment changed neither body weights nor liver and gastrocnemius weights, but succeeded in reducing the weight of peri-epididymal adipose tissues. Triacylglycerol contents were lowered in liver and ketone body concentrations were found slightly more elevated in blood. In the liver, mitochondrial carnitine palmitoyltransferase I (CPT I) exhibited a slightly higher specific activity and a lower sensitivity to malonyl-CoA inhibition, while peroxisomal fatty acid oxidizing system (PFAOS) was found to be less active. Carnitine supplied for one month reduced the mass of the periepididymal fat tissue, but not those of the other studied organs, and produced a slight but non-significant gain in body weight after ten days of treatment. In the liver, CPTI characteristics were comparable in control and treated groups, while PFAOS activity was less in rats receiving carnitine. Data show that L-carnitine at a low level in the diet exerted two paradoxical effects before and after ten days of treatment. Results are discussed in regard to fatty acid oxidation in mitochondria and peroxisomes, and to the possible altered acyl-CoA/acylcarnitine ratio with increased concentrations of L-carnitine in the liver.

Octadecatrienoic acids as the substrates for the key enzymes in glycerolipid biosynthesis and fatty acid oxidation in rat liver

The activities of key enzymes in glycerolipid biosynthesis and fatty acid oxidation were compared using CoA esters of naturally occurring positional isomers of octadecatrienoic acids (18:3) as the substrates. The trienoic acids employed were 9,12,15-18:3 (alpha-18:3), 6,9,12-18:3 (gamma-18:3), and 5,9,12-18:3 (pinolenic acid which is a fatty acid contained in pine seed oil, po-18:3). The activities of microsomal glycerol 3-phosphate acyltransferase obtained with various 18:3 were only slightly lower than or comparable with those obtained with palmitic (16:0), oleic (18:1), and linoleic (18:2) acids. Mitochondrial glycerol 3-phosphate acyltransferase was exclusively specific for saturated fatty acyl-CoA. The activities of microsomal diacylglycerol acyltransferase measured with various polyunsaturated fatty acyl-CoAs were significantly lower than those obtained with 16:0- and 18:1-CoAs. Among the polyunsaturated fatty acids, gamma-18:3 gave the distinctly low activity. The Vmax values of the mitochondrial carnitine palmitoyltransferase I were significantly higher with alpha-18:3 and po-18:3 but not gamma-18:3, than with 16:0 and 18:2, while the apparent Km values were the same irrespective of the types of acyl-CoA used except for the distinctly low value obtained with gamma-18:3. The response to an inhibitor of the acyltransferase reaction, malonyl-CoA, was appreciably exaggerated with 18:2, alpha-18:3, and po-18:3 more than with 16:0 and 18:1. However, the response with gamma-18:3 was the same as with 16:0. Thus, some of glycerolipid biosynthesis and fatty acid oxidation enzymes could discriminate not only the differences in the degree of unsaturation of fatty acids but also the positional distribution of double bond among the naturally occurring 18:3 acids.

Enhancement of activities relative to fatty acid oxidation in the liver of rats depleted of L-carnitine by D-carnitine and a gamma-butyrobetaine hydroxylase inhibitor

This study was designed to examine whether the depletion of L-carnitine may induce compensatory mechanisms allowing higher fatty acid oxidative activities in liver, particularly with regard to mitochondrial carnitine palmitoyltransferase I activity and peroxisomal fatty acid oxidation. Wistar rats received D-carnitine for 2 days and 3-(2,2,2,-trimethylhydrazinium)propionate (mildronate), a noncompetitive inhibitor of gamma-butyrobetaine hydroxylase, for 10 days. They were starved for 20 hr before being sacrificed. A dramatic reduction in carnitine concentration was observed in heart, skeletal muscles and kidneys, and to a lesser extent, in liver. Triacylglycerol content was found to be significantly more elevated on a gram liver and whole liver basis as well as per mL of blood (but to a lesser extent), while similar concentrations of ketone bodies were found in the blood of D-carnitine/mildronate-treated and control rats. In liver mitochondria, the specific activities of acyl-CoA synthetase and carnitine palmitoyltransferase I were enhanced by the treatment, while peroxisomal fatty acid oxidation was higher per gram of tissue. It is suggested that there may be an enhancement of cellular acyl-CoA concentration, a signal leading to increased liver fatty acid oxidation in acute carnitine deficiency.

Involvement of microsomal vesicles in part of the sensitivity of carnitine palmitoyltransferase I to malonyl-CoA inhibition in mitochondrial fractions of rat liver

Liver mitochondrial fractions as normally isolated contain only 10-20% of total mitochondria and may not be representative of the whole mitochondrial population. This study was designed to evaluate the dependence of the sensitivity of carnitine palmitoyl-transferase I (CPT I) to malonyl-CoA inhibition in mitochondrial fractions that are not normally studied. Four fractions prepared from rat liver were found to be contaminated to different extents by microsome vesicles, on the basis of marker-enzyme activities and micrographic data. Purification of mitochondrial fractions on a Percoll gradient decreased to some extent the microsomal contamination, which was due in part to the existence of close bonds between microsomes and the outer membranes of mitochondria. A greater degree of contamination of mitochondrial fractions by microsomes was correlated with a greater sensitivity of CPT I to malonyl-CoA inhibition. Attempts were made to enhance the sensitivity of CPT I to malonyl-CoA with the use of microsomes. Measurements performed by adding mitochondria and microsomes in the same CPT I assay failed to demonstrate any significant enhancement of malonyl-CoA inhibition. However, addition of ATP to a mixture of mitochondria and microsomes was shown to trigger the binding of both particles, as assessed by enzymic and micrographic data, and to increase the sensitivity of CPT I to malonyl-CoA inhibition. These results demonstrated that the binding of microsomes to mitochondria, unlike the simple mixing of both particles, was capable of altering the sensitivity of CPT I to malonyl-CoA. The data also suggest that this process could be of physiological importance, owing to the frequency of contiguous zones between mitochondria and endoplasmic reticulum observed in sections of intact liver cells.

Effect of dietary n-3 and n-6 polyunsaturated fatty acids on lipid-metabolizing enzymes in obese rat liver

This study was designed to examine whether n-3 and n-6 polyunsaturated fatty acids at a very low dietary level (about 0.2%) would alter liver activities in respect to fatty acid oxidation. Obese Zucker rats were used because of their low level of fatty acid oxidation, which would make increases easier to detect. Zucker rats were fed diets containing different oil mixtures (5%, w/w) with the same ratio of n-6/n-3 fatty acids supplied either as fish oil or arachidonic acid concentrate. Decreased hepatic triacylglycerol levels were observed only with the diet containing fish oil. In mitochondrial outer membranes, which support carnitine palmitoyltransferase I activity, cholesterol content was similar for all diets, while the percentage of 22:6n-3 and 20:4n-6 in phospholipids was enhanced about by 6 and 3% with the diets containing fish oil and arachidonic acid, respectively. With the fish oil diet, the only difference found in activities related to fatty acid oxidation was the lower sensitivity of carnitine palmitoyltransferase I to malonyl-CoA inhibition. With the diet containing arachidonic acid, peroxisomal fatty acid oxidation and carnitine palmitoyltransferase I activity were markedly depressed. Compared with the control diet, the diets enriched in fish oil and in arachidonic acid gave rise to a higher specific activity of aryl-ester hydrolase in microsomal fractions. We suggest that slight changes in composition of n-3 or n-6 polyunsaturated fatty acids in mitochondrial outer membranes may alter carnitine palmitoyltransferase I activity.

Preferential reduction in adipose tissue alpha-linolenic acid (18:3 omega 3) during very low calorie dieting despite supplementation with 18:3 omega 3

We have previously reported that the relative content of 18:3 omega 3 in adipose triglyceride (TG) of women was reduced following major weight loss while on a very low calorie diet (VLCD). In an attempt to prevent this loss of 18:3 omega 3 reserves, we have tested two VLCD supplemented with varying amounts of 18:3 omega 3. The formula (FORM) and food VLCD (2.1-3.0 MJ or 500-700 kcal/d) contained 20 g/d of fat and provided the recommended dietary allowance for minerals and vitamins. FORM subjects (Group 1) were 5 women [initial body mass index (BMI) of 36.8, 168% ideal body weight (IBW) who received 20 g/d of canola oil (1.6 g 18:3 omega 3). Their mean weight loss was 23.9 kg in a 4-5 mon period. Food VLCD subjects (Group 2) were 6 women (BMI 33.9, 155% IBW) supplemented with 2 g/d of linseed oil (1.1 g 18:3 omega 3). Their mean weight loss was 17.4 kg in a 2-3 mon period. Needle biopsies of adipose tissue were obtained from Group 1 before, at midpoint and after weight loss; and from Group 2 before and after weight loss. The adipose TG and serum (Group 1) were separated and their fatty acid composition determined by thin-layer and gas chromatography. In Group 1, adipose 18:3 omega 3 fell from 0.65 to 0.59 wt%, then to 0.52 wt% during weight loss. In Group 2, it fell from 0.77 to 0.64 wt%. The fall in adipose 18:3 omega 3 with weight loss was significant at P = 0.01 (Group 1) and P < 0.01 (Group 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Utilization of extracellular lipids by HT29/219 cancer cells in culture

Uptake and incorporation of long-chain fatty acids were studied in a human colorectal cancer cell line (HT29/219) grown in culture medium supplemented with either fetal calf serum (FCS) or horse serum (HS). The cells were grown for 120 h with no change of medium; the two major cellular lipid classes, the phospholipids and the triacylglycerols, were analyzed at regular time-points. We observed significant changes in the concentration of most fatty acids throughout culture, and differences in their composition when different sera were used to supplement the medium. Minimal levels of free fatty acids were found in the cells, indicating a very small "free fatty acid pool". A major difference between the cells grown in media supplemented with different sera was the changes observed in concentrations of cellular polyunsaturated fatty acids during growth. In cells grown with FCS (in which 20:4n-6 is present), the levels of this acid in the phospholipid and triacylglycerol fractions declined rapidly during cell growth, suggesting further metabolism. In cells grown in medium supplemented with HS, 18:2n-6 was the major polyunsaturated acid present. There was clear evidence that this acid accumulated in the cellular triacylglycerol and phospholipid fractions. Furthermore, its concentration did not decline during growth in culture, suggesting minimal conversion to other polyunsaturated n-6 acids. Our results suggest that fatty acids from additional sources in the medium, for example triacylglycerols and phospholipids associated with the lipoproteins, are taken up by the cells. There is also indication of cellular fatty acid synthesis, particularly of monounsaturated and saturated acids during the culture period.(ABSTRACT TRUNCATED AT 250 WORDS)

Docosahexaenoic acid in developing brain and retina of piglets fed high or low α-linolenate formula with and without fish oil

Docosahexaenoic acid (22:6n-3) can be synthesized in the liver and/or brain from alpha-linolenic acid (18:3n-3) and is required in large amounts in structural membranes of developing brain and retina. The adequacy and efficacy of formulas containing 18:3n-3 and/or fish oil in providing 22:6n-3 for deposition was investigated in piglets fed formula from birth to 15 days. The test formulas contained high (HL) or low (LL) 18:3n-3 (3.9 or 0.7% of the total formula fatty acids, respectively), or low 18:3n-3 plus fish oil (LL+FO) to provide C20 and C22 n-3 polyunsaturated fatty acids (0.8% of total fatty acids). Fatty acid analyses of synaptic plasma membrane and retina ethanolamine phospholipids (EPL), which are especially enriched in 22:6n-3, were compared to those of 15-day-old piglets fed sow milk (SM). Feeding LL resulted in lower 22:6n-3 in synaptic plasma membrane. Fatty acid levels in HL and LL+FO piglets were equivalent to SM, with the exception of lower 22:5n-3 in the synaptic plasma membrane of LL+FO and in the retina of HL and LL+FO-fed piglets. Levels of 22:4n-6 were also lower in the retina of the LL+FO group. The results suggest formula 18:3n-3 is at least 24% as effective as C20 and C22 n-3 fatty acids as a source of membrane 22:6n-3. This study shows dietary 18:3n-3, as the only n-3 fatty acid, can support deposition of comparable percentage of 22:6n-3 to natural milk. Fish oil also supported tissue levels of 22:6n-3 similar to natural milk; however, lower 22:4n-6 may indicate possible inhibitory effects on n-6 metabolism.

Rat liver outer mitochondrial carnitine palmitoyltransferase activity towards long-chain polyunsaturated fatty acids and their CoA esters

The activity of the overt form of rat liver mitochondrial carnitine palmitoyltransferase or CPT0 (EC 2.3.1.21) towards different fatty acid substrates was studied. The following non-esterified fatty acids (NEFA) and their CoA esters in the presence of 1% bovine serum albumin (BSA) were tested: 16:0, 18:0, 18:1, 18:2, 18:3 omega 3, 20:4, 20:5 omega 3 and 22:6 omega 3. The data fit a square hyperbolic model for enzyme catalysis (p less than 0.001, non-linear regression). Asymptotic Vmax and K0.5, substrate concentration at one-half Vmax, were calculated using total concentrations of acyl-CoA, or unbound concentrations of NEFA. BSA was found to act as a true substrate reservoir for NEFA in that the dissociation of the NEFA-BSA complex was 10-330 times faster than the CPT0 reaction. Regardless of form (NEFA or CoA ester), 18:3 omega 3 gave the highest, while 22:6 omega 3 and 18:0 gave the lowest rates of acylcarnitine synthesis. Except for 18:3 omega 3 and 18:2, Vmax for NEFA was generally lower than for acyl-CoA, with the greatest differences observed for 20:4, 20:5 omega 3 and 22:6 omega 3, suggesting that acyl-CoA synthesis may also be important in the control of the entry of these fatty acids into the mitochondria. The data provide an enzymatic rationale for the relatively low content of 18:3 omega 3 in esterified lipid.

Effects of oleic, arachidonic and 5,8,11,14-nonadecatetraenoic acids on lipid secretion and ketogenesis in perfused rat liver

The effects of perfused oleic (18:1n-9), arachidonic (20:4n-6) and 5,8,11,14-nonadecatetraenoic (19:4n-5) acids on triglyceride and cholesterol secretion and ketone body production were studied in isolated rat liver. As compared to oleic and 19:4n-5 acids, both ketone body production and triglyceride secretion were significantly lowered when arachidonic acid was perfused. The concentration of triglyceride in the post-perfused liver was lower upon perfusion with arachidonic acid than upon perfusion with oleic acid or 19:4n-5 acid. Cholesterol secretion in the liver perfused with arachidonic acid or 19:4n-5 acid was significantly higher than with oleic acid. The concentration of cholesterol in the post-perfused liver was slightly but significantly higher with 19:4n-5 acid than with the other fatty acids. The results suggest that 19:4n-5 acid when compared with arachidonic acid affects lipid metabolism in liver differently.