A method for specific analysis of free fatty acids in biological samples by capillary gas chromatography

The profile of plasma non-esterified fatty acids in children with different terms of type 1 diabetes mellitus

Composition and quantitative content of non-esterified fatty acids (NEFA) were investigated in plasma samples of healthy children (12) and children with type 1 diabetes mellitus (DM1) (31) by gas chromatography (GC) after preliminary NEFA solid-phase extraction from plasma lipids. There was a significant (p<0.001) 1.6-fold increase in the total level of NEFA regardless of the disease duration. In the group of DM1 children with the disease period less than 1 year there was an increase in the arachidonic acid (20:4) content (30%) and the oleic acid trans-isomer (18:1) content (82%), and also a decrease in the docosahexaenoic acid (22:6 n3) content (26% ) and the docosapentaenoic acids (22:5 n-6) content (60%). In the group of DM1 children with prolonged course of this disease the altered NEFA levels returned to the normal level

[Non-esterified fatty acids of blood serum in type 1 diabetic women during late pregnancy]

Using gas chromatography a comparative study of the range and content of individual non-esterified fatty acids in serum of patients with diabetes mellitus type 1 in the third trimester of pregnancy, and healthy pregnant and non-pregnant women has been carried out. In groups of pregnant women there was activation of lipid metabolism, confirmed by corresponding changes in serum biochemical parameters, as well as in the content of non-esterified fatty acids. Intergroup differences in the non-esterified fatty acids were not found. However, there were significant differences between the examined groups in the quantitative content of non-esterified fatty acids.

Erythrocyte membrane and plasma non-esterified n-3 and n-6 polyunsaturated fatty acids of pregnant and non-pregnant Brazilian adolescents

The aim of the present study was to evaluate the influence of pregnancy in adolescents on the fatty acid composition of the erythrocyte membrane, which was used as a proxy for status of n-3 and n-6 polyunsaturated fatty acids (PUFA), and also on the composition of plasma non-esterified fatty acids (NEFA) mobilized from the adipose tissue. Two matched groups of healthy adolescents (14-19 years) from Rio de Janeiro, Brazil, were compared: pregnant (n=26; 32.7+/-3.9 weeks of gestation, mean+/-SD) and non-pregnant (n=20). Blood samples were collected after an overnight fast. Mean dietary intakes of total fat and n-3 and n-6 PUFA (energy %) were not different between pregnant and non-pregnant adolescents, and the consumption of food sources of docosahexaenoic acid (DHA) was low. Fasting total NEFA and NEFA 18:2n-6, 18:3n-6 and 20:4n-6 (g/100g fatty acids) were higher in pregnant than in non-pregnant adolescents. Although erythrocyte 20:4n-6 was lower in pregnant adolescents, there were no differences in DHA (g/100g fatty acids), in DHA status indices (22:5n-6/22:4n-6 and 22:6n-3/22:5n-6 ratios) and in the index of n-3+n-6 PUFA status ([Sigman-3+Sigman-6]/[Sigman-7+Sigman-9]) in erythrocytes as compared with those of non-pregnant adolescents. In conclusion, pregnancy did not have an adverse effect on erythrocyte DHA content or on DHA and n-3+n-6 PUFA status indices in the adolescents studied.

Essential and long-chain polyunsaturated fatty acid status and fatty acid composition of breast milk of lactating adolescents

The aims of the present study were to evaluate essential fatty acids (EFA) and long-chain PUFA (LCPUFA) status in lactating adolescents and its association with breast milk composition. Healthy nursing adolescents from Rio de Janeiro, Brazil (n 30; 14-19 years; 30-120 d postpartum), exclusively or predominantly breast-feeding, participated in this study. Breast milk and blood samples were collected after overnight fasting. Fatty acid composition of breast milk, erythrocyte membrane (EM) and plasma NEFA were determined by GC. Indices of fatty acid status (mean melting point (MMP); EFA status index; DHA status indices, 22 : 5n-6:22 : 4n-6 and 22 : 6n-3:22 : 5n-6 ratios) were calculated from EM fatty acid composition. Dietary intake of n-3 fatty acids was low when compared with current recommendations for lactating women. MMP was associated with indices of DHA status, some individual fatty acids in EM and years post-menarche and weeks postpartum, suggesting the use of erythrocyte MMP as a possible comprehensive biochemical marker of LCPUFA status in this physiological condition. The DHA status of lactating adolescents and their milk DHA concentrations were similar to the values of Brazilian lactating adults, but lower compared with the values of lactating adults from other countries. Therefore, these lactating adolescents were apparently not disadvantaged, as compared with the Brazilian adults, when EM and breast milk fatty acid composition were considered. In general, PUFA in milk from adolescents presented few associations with their concentrations in plasma NEFA and with maternal status. However, milk DHA was associated with maternal LCPUFA and DHA states.

Polyunsaturated fatty acids and conjugated linoleic acid isomers in breast milk are associated with plasma non-esterified and erythrocyte membrane fatty acid composition in lactating women

Maternal adipose tissue is a major contributor to breast milk long-chain fatty acids, probably through the pool of plasma NEFA. The fatty acid composition of the erythrocyte membrane (EM) is a biochemical index of the intake of fatty acids not synthesized endogenously and of PUFA and long-chain PUFA fatty acid status. The present study investigated the associations between breast milk fatty acid composition and the composition of plasma NEFA and of EM fatty acids with special reference to PUFA, long-chain PUFA and conjugated linoleic acid (CLA). The detailed fatty acid composition of mature breast milk was also reported. Thirty-three healthy, lactating Brazilian women donated milk samples; of these, twenty-four also donated blood samples in an observational cross-sectional study. Breast milk fatty acid composition presented several associations with NEFA and EM composition, which explained most (> or =50 %) of the variability of selected milk PUFA, long-chain PUFA and CLA. Milk CLA was associated with fatty acids that are markers of dairy fat intake in the diet, NEFA and EM. In general, breast milk n-3 fatty acids and CLA, but not n-6 fatty acids, were associated with EM composition, whereas both the n-6 and n-3 fatty acids and CLA in milk were associated with NEFA composition, possibly owing to its role as a direct source of fatty acids for breast milk. These findings emphasize the contribution of the NEFA pool derived from the adipose tissue to the long-chain fatty acid composition of breast milk.

Role of the cyclic AMP-dependent pathway in free radical-induced cholesterol accumulation in vascular smooth muscle cells

We have previously reported that free radical-treated vascular smooth muscle cells (SMC) lead to cholesterol accumulation in vitro. In the current study, we investigated the effects of oxidative stress on cyclic AMP concentration and cAMP-dependent enzymes involved in cholesterol homeostasis in A7r5 cells. Under our conditions of a mild oxidative stress, namely with no change in cell viability, we found that free radicals, initiated using azobis-amidinopropane dihydrochloride (AAPH), resulted in a dose-dependent decrease in cellular cAMP which was opposed by vitamin E preincubation. Although the addition of adenylate cyclase activators (carbacyclin and forskolin) increased cAMP levels it did not succeed in restoring the AAPH-induced decrease. The oxidative stress-induced increase in activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase and of acyl coenzyme A: cholesterol acyltransferase and the decrease in neutral cholesteryl ester hydrolase activity were suppressed by addition of dibutyryl cAMP. Taken together, these results strongly suggest that free radicals reduce cAMP concentrations by altering cell membrane adenylate cyclase activity. The changes of cAMP-dependent enzymes induced by oxidative stress resulting in cholesterol accumulation might be one of the processes leading to SMC-derived foam cells depicted in atheroma plaque. Moreover, if extrapolated to in vivo, these data may explain in part the beneficial effects of antioxidants in the reduction of cardiovascular diseases.

Oxidative stress leads to cholesterol accumulation in vascular smooth muscle cells

The transformation of macrophages and smooth muscle cells into foam cells by modified low-density lipoproteins (LDL) is one of the key events of atherogenesis. Effects of free radicals have mainly been studied in LDL, and other than toxicity, data dealing with direct action of free radicals on cells are scarce. This study focused on the direct effects of free radicals on cholesterol metabolism of smooth muscle cells. A free radical generator, azobis-amidinopropane dihydrochloride, was used, and conditions for a standardized oxidative stress were set up in vascular smooth muscle cells. After free radical action, the cells presented an accumulation of cholesterol that appeared to be the result of: (i) an increase in cholesterol biosynthesis and esterification; (ii) a decrease in cell cholesteryl ester hydrolysis; and (iii) a reduced cholesterol efflux. All these parameters were opposed by antioxidants. In addition, oxidant stress induced an increased degradation of acetyl-LDL, whereas no change was noted for native LDL. From this data, it was concluded that cholesterol metabolism of vascular smooth muscle cells was markedly altered by in vitro treatment with free radicals, although cell viability was unaffected. The resulting disturbance in cholesterol metabolism favors accumulation of cholesterol and cholesteryl esters in vascular cells, and thus may contribute to the formation of smooth muscle foam cells.

A semiautomated enzymatic method for determination of nonesterified fatty acid concentration in milk and plasma

An enzymatic assay for the determination of nonesterified fatty acid concentrations in milk and plasma is described. The procedure is semiautomated for use with a plate luminometer or plate spectrophotometer and enables routine batch processing of large numbers of small samples (< or =5 microL). Following the activation of nonesterified fatty acids (NEFA) by acylCoA synthetase, the current assay utilizes UDP-glucose pyrophosphorylase to link inorganic pyrophosphate to the production of NADH through the reactions catalyzed by phosphoglucomutase and glucose-6-phosphate 1-dehydrogenase. With this assay sequence the formation of NADH from NEFA is complete within 50 min at 37 degrees C. Enzymatic spectrophotometric techniques were unsuitable for NEFA determination in human milk due to the opacity of the sample. The use of the NADH-luciferase system has overcome this problem, allowing the enzymatic determination of NEFA in human milk. Sample collection and treatment procedures for milk and plasma have been developed to prevent enzymatic lipolysis and to limit interference from enzymes present in milk. The recovery of palmitic acid added to milk and plasma samples was 94.9+/-2.9 and 100+/-4.5%, respectively. There was no difference (P = 0.13) in plasma NEFA concentrations determined by the current method and a commercially available enzymatic spectrophotometric technique (Wako NEFA-C kit). Plasma NEFA concentrations determined by gas chromatography were 28% higher compared to both the Wako NEFA-C kit and the current method.

Fuel choices by human platelets in human plasma

Despite the fact that homogeneous preparations of isolated cells are now being used very effectively to study a range of important biochemical questions, it is still not known what combination of fuels and energy-producing pathways is used by cells when offered the complex mixture characteristic of plasma or extracellular fluid. We have developed an in vitro system whereby highly purified and functional human platelets are incubated in human plasma that has been minimally modified from its native state. The concentration of platelets and fuels, and the complexity of fuels in the incubation are similar to those in vivo. The preparation thus represents a reasonable approximation of the physiological condition, considering the complex nature of the system being studied. Measurements carried out simultaneously during the incubation are rates of oxygen consumption, lactate production and fuel oxidation. The data allow the calculation of total ATP turnover, and contributions to this turnover by lactate production and the oxidation of individual fuels. Lactate production accounts for 24% of the ATP turnover. The oxidation of glucose and 3-hydroxybutyrate each account for under 5%, palmitate for 21%, oleate for 7% and acetate for 9%, leaving 32% of the ATP turnover as yet unaccounted for. The results confirm some previous measurements in the literature, but show that data collected under non-physiological experimental conditions can be misleading.

Arachidonate transport through the blood-retina and blood-brain barrier of the rat during aging

The permeability-surface area product (PS) of [I-14C]arachidonate at the blood-retina (BRB) and blood-brain barrier (BBB) was determined after short carotid perfusion in Wistar rats at 4, 12 and 28 months of age. For the visual system structures, parietal and frontal cortex, striatum, hypothalamus, hippocampus and olfactory bulb there was no significant difference among mean PSs in any age group. Our results indicate that: (1) arachidonate is able to cross at relevant rate BRB and BBB; (2) in all brain regions except retina, optic tract and hippocampus, blood barriers have a transport capacity for arachidonate significantly higher than that for docosahexaenoate and palmitate as well; (3) aging does not affect influx into retina and other structures of rat central nervous system of the arachidonate, a metabolic substrate rapidly incorporated into microcapillary and brain lipids, and for which simple diffusion transport across the BRB and BBB may be postulated.

Enhanced platelet thromboxane synthesis and reduced macrophage-dependent fibrinolytic activity related to oxidative stress in oral contraceptive-treated female rats

In previous studies conducted in rats and in women, we have shown that oral contraceptive (OC) administration induced a platelet hyperaggregation simultaneously with an increased platelet lipid biosynthesis which might be related to lipid peroxidation. In the present study, we specifically studied the arachidonic acid and the fibrinolytic pathways in relation to the fatty acid composition in female rats treated for 6 weeks with OC (ethinyl estradiol plus lynestrenol). We found that platelets of treated animals were not only hyper-responsive to thrombin and ADP, but also to sodium arachidonate. In addition, the results of the thrombin-induced release of labeled arachidonic acid pre-incorporated into platelet membrane phospholipids showed an increased biosynthesis of lipoxygenase and cyclooxygenase metabolites after OC treatment. These data indicated a stimulated platelet arachidonate metabolism in OC animals compared to controls which was further confirmed by the increased thrombin-induced production of thromboxane B2 (TXB2) as measured with a radioimmunoassay. The platelet thrombin-stimulated TXB2 biosynthesis was inhibited in vitro in the presence of 500 mu M aspirin and 1 mM vitamin E; the erythrocytes from OC animals compared with controls presented an enhanced in vitro susceptibility to free radical-induced hemolysis. These data indicated that a free radical mediated-process might occur. This hypothesis is confirmed by an increase of plasma lipid peroxidation parameters (conjugated dienes, lipid peroxides, thiobarbituric acid reactive substances). After OC-treatment, a decrease in plasma and platelet long chain polyunsaturated fatty acids, particularly (n-3), is in keeping with this idea. Furthermore, the results of the peritoneal macrophage-dependent fibrinolytic activity indicated that OC induced a drastic decrease in urokinase plasminogen activator activity which might further contribute to the platelet hyperactivity. Altogether these data suggest that besides the reported increase in clotting factors, platelet hyperactivity, possibly through a stimulated free radical-induced arachidonic acid metabolism, might be involved in the known high thrombogenic risk observed in OC users.

Increased cholesteryl ester transfer activity in plasma from analbuminemic patients

Hypercholesterolemia associated with analbuminemia, an inherited disease manifesting low plasma albumin concentration, is characterized by enhanced LDL cholesterol levels and reduced HDL cholesterol levels. In addition, compared with normal counterparts, the esterified cholesterol:triglyceride ratio tends to be higher in analbuminemic apoB-containing lipoproteins and lower in analbuminemic HDL. The aim of the present study was to investigate the mechanism that may account for the association of a hypoalbuminemic state with alterations in the concentration and composition of plasma lipoprotein fractions. To this end, endogenous cholesterol esterification activity, phospholipid transfer activity, and cholesteryl ester transfer activity were measured in total plasma from three analbuminemic patients and five control subjects. Whereas endogenous cholesterol esterification and phospholipid transfer rates were not significantly affected in analbuminemia, the transfer of radiolabeled cholesteryl esters from HDL toward apoB-containing lipoproteins was constantly higher in analbuminemic plasmas than in normal control plasma (473.6+/-107.3% x h(-1) x mL(-1) versus 227.5+/-84.0% x h(-1) x mL(-1), respectively; P=.036). The rise in cholesteryl ester transfer protein (CETP) activity in analbuminemic plasma was due to a significant increase in the transfer of radiolabeled cholesteryl esters toward LDL but not toward the triglyceride-rich lipoproteins. The CETP mass was higher in analbuminemic patients than in control subjects, but the difference did not reach the significance level (5.18+/-0.82 mg/L versus 3.13+/-1.19 mg/L respectively; P=.07). Since abnormally elevated nonesterified fatty acid (NEFA) levels were shown to be associated with analbuminemic lipoproteins, mostly LDL, the direct role of lipoprotein-bound NEFA in enhancing CETP activity was suspected. In support of this view, supplementation of total plasmas with fatty acid-poor albumin was shown to reduce CETP activity to a significantly greater extent in analbuminemic plasmas than in normal control plasma. It is concluded that hyperlipidemia associated with the hypoalbuminemic state can relate, at least in part, to the combined effect of CETP and NEFA in promoting the transfer of cholesteryl esters from the antiatherogenic HDL toward the proatherogenic apoB-containing lipoproteins.

Evidence for nonesterified fatty acids as modulators of neutral lipid transfers in normolipidemic human plasma

The relations between the level of plasma nonesterified fatty acid (NEFA) and both the mass concentration and activity of the cholesteryl ester transfer protein (CETP) were studied in fasted normolipidemic subjects. Plasma NEFA correlated positively with both CETP mass concentration (r = .50; P < .01) and the transfer of cholesteryl ester from HDL toward plasma VLDL+LDL (CETHDL-->VLDL+LDL activity) (r = .46; P < .05) but not with the transfer of cholesteryl ester from LDL toward plasma HDL (CETLDL-->HDL activity) (r = .05; NS). The high binding capacity of albumin for NEFA was used to investigate whether lipoprotein-bound NEFAs were implicated in the modulation of the cholesteryl ester transfer reaction. As compared with nonsupplemented controls, the addition of an excess of fatty acid-free albumin (8 g/L) to total normolipidemic plasmas reduced CETHDL-->VLDL+LDL activity (18.3 +/- 5.5% versus 9.8 +/- 3.1%; P < .0001) but not CETLDL-->HDL activity (22.3 +/- 4.5% versus 23.3 +/- 5.1%; NS). Moreover, CETHDL-->VLD+LDL and CETLDL-->HDL activities correlated negatively when measured in native plasma (r = -.45; P < .05) but positively when measured in albumin-supplemented plasma (r = .40; P < .05). In long-term incubation experiments, lipoprotein-bound NEFA increased the net mass transfer of cholesteryl esters from HDL toward VLDL+LDL but reduced the net mass transfer of triglycerides in the opposite direction, from VLDL+LDL toward HDL. Taken together, data of the present study brought strong and concordant arguments in favor of a dual effect of plasma NEFA in modulating both the mass and the activity of CETP in vivo.

Mechanism of activation and functional significance of the lipolysis-stimulated receptor. Evidence for a role as chylomicron remnant receptor

In cultured human and rat cells, the lipolysis-stimulated receptor (LSR), when activated by free fatty acids (FFA), mediates the binding of apoprotein B- and apoprotein E-containing lipoproteins and their subsequent internalization and degradation. To better understand the physiological role of LSR, we developed a biochemical assay that optimizes both the activation and binding steps and, thus, allows the estimation of the number of LSR binding sites expressed in the livers of living animals. With this technique, a strong inverse correlation was found in rats between the apparent number of LSR binding sites in liver and the postprandial plasma triglyceride concentration (r = -0.828, p < 0.001, n = 12). No correlation existed between the number of LSR and plasma triglycerides measured in the same animals after 24 h of fasting. The same membrane binding assay was used to elucidate the mechanism by which FFA induce lipoprotein binding to LSR. The LSR activation step was mediated by direct interaction of FFA with LSR candidate proteins of apparent molecular masses of 115 and 90 kDa and occurred independently of the membrane lipid environment. The FFA-induced conformational shift that revealed the lipoprotein binding site remained fully reversible upon removal of the FFA. However, occupancy of the site by the apoprotein ligand stabilized the active form of LSR. Comparison of the effect of different FFA alone or in combination indicated that the same binding site is revealed by different FFA and that the length and saturation of the FFA monomeric carbon chain are critical in determining the potency of the FFA activating effect. We propose that the LSR pathway represents a limiting step for the cellular uptake of intestinally derived triglyceride-rich lipoproteins and speculate that FFA liberated by lipolysis initiate this process by altering the conformation of LSR to reveal the lipoprotein binding site.

Determination of plasma non-esterified fatty acids and triglyceride fatty acids by gas chromatography of their methyl esters after isolation by column chromatography on silica gel

Non-esterified fatty acids (NEFA) and triglycerides were isolated from human plasma by column chromatography on silica gel. Eight principal fatty acids of each of these lipid classes were determined by gas chromatography of their methyl ester derivatives and quantified relative to multipoint standard curves. Within-day relative standard deviations for plasma non-esterified fatty acid and triglyceride fatty acid determinations were 2.4 and 3.2%, respectively. Day-to-day relative standard deviations for plasma non-esterified fatty acid and triglyceride fatty acid determinations were 1.4 and 1.1%, respectively. The total plasma concentration and the relative proportions of the eight non-esterified fatty acids determined by this method were significantly different from results obtained according to two generally accepted methods for direct plasma non-esterified fatty acid determination without a specific isolation step. These comparisons suggested that considerable fatty acid ester lipid hydrolysis occurred during these direct determination procedures, and that this hydrolysis resulted in 3-fold overestimation of plasma NEFA content by those methods. Measured levels of arachidonic acid are substantially overestimated by these direct determination methods in which non-esterified fatty acids are not isolated before derivatization.