Effect of randomly interesterified triacylglycerol containing medium- and long-chain fatty acids on hepatic fatty acid oxidation after a single administration to rats

MLCTs, which are randomly interesterified triacylglycerol containing medium- and long-chain fatty acids in the same glycerol molecule, showed significantly higher acyl-CoA dehydrogenase activity when measured by using butyryl-CoA, octanoyl-CoA, and palmitoyl-CoA as substrates than long-chain triacylglycerol one hour after a single administration to rats. These results suggest that not only medium-chain fatty acid oxidation, but also long-chain fatty acid oxidation were increased in the liver of rats administered with MLCT.     

Randomly interesterified triacylglycerol containing medium- and long-chain fatty acids stimulates fatty acid metabolism in white adipose tissue of rats

We have reported previously that randomly interesterified triacylglycerol containing medium- and long-chain fatty acids in the same glycerol molecule (MLCT) resulted in significantly lower body fat accumulation and higher hepatic fatty acid oxidation than from long-chain triacylglycerol (LCT) in rats. To understand the metabolic changes occurring in white adipose tissue, the fatty acid oxidation and synthesis, and the adipocytokine level were measured in rats fed with MLCT or LCT for 2 weeks. In comparison with LCT, MLCT lowered not only the fatty acid synthase and glycerol-3-phosphate dehydrogenase activities in perirenal adipose tissue, but also the serum insulin and leptin levels, in addition to significantly reducing the body fat accumulation. In contrast, fatty acid oxidation measured as the carnitine palmitoyltransferase activity in the tissue was significantly higher in the MLCT-fed rats than in the LCT-fed rats. It seems that the altered fatty acid metabolism in adipose tissue per se was also responsible for the lower adiposity by dietary MLCT.     

Contrasting metabolic effects of medium- versus long-chain fatty acids in skeletal muscle

Dietary intake of long-chain fatty acids (LCFAs) plays a causative role in insulin resistance and risk of diabetes. Whereas LCFAs promote lipid accumulation and insulin resistance, diets rich in medium-chain fatty acids (MCFAs) have been associated with increased oxidative metabolism and reduced adiposity, with few deleterious effects on insulin action. The molecular mechanisms underlying these differences between dietary fat subtypes are poorly understood. To investigate this further, we treated C2C12 myotubes with various LCFAs (16:0, 18:1n9, and 18:2n6) and MCFAs (10:0 and 12:0), as well as fed mice diets rich in LCFAs or MCFAs, and investigated fatty acid-induced changes in mitochondrial metabolism and oxidative stress. MCFA-treated cells displayed less lipid accumulation, increased mitochondrial oxidative capacity, and less oxidative stress than LCFA-treated cells. These changes were associated with improved insulin action in MCFA-treated myotubes. MCFA-fed mice exhibited increased energy expenditure, reduced adiposity, and better glucose tolerance compared with LCFA-fed mice. Dietary MCFAs increased respiration in isolated mitochondria, with a simultaneous reduction in reactive oxygen species generation, and subsequently low oxidative damage. Collectively our findings indicate that in contrast to LCFAs, MCFAs increase the intrinsic respiratory capacity of mitochondria without increasing oxidative stress. These effects potentially contribute to the beneficial metabolic actions of dietary MCFAs.     

Kinetics of the inhibition of hog kidney D-amino acid oxidase by short-, medium- and long-chain fatty acids

Various fatty acids were studied in vitro as inhibitors of pure hog kidney D-amino acid oxidase by means of a spectrophotometric peroxidase-coupling method using D-methionine as a substrate. All the fatty acids tested behaved as substrate-competitive inhibitors of the enzyme. The affinity of the saturated aliphatic acids for D-amino acid oxidase decreased from pentanoate (5:0; Ki = 220 microM) to laurate (12:0; Ki = 675 microM), then rose to a maximum with stearate (18:0; Ki = 36 microM), suggesting the presence of a site in the active center of the enzyme that accepts long-chain fatty acid alkyl groups. Unsaturation did not further increase the affinity of the fatty acid for this binding site.     

Transesterification reaction between medium- and long-chain fatty acid triglycerides using surfactant-modified lipase

Transesterification between medium-chain fatty acid triglycerides (MCT) and long-chain fatty acid triglycerides (LCT) in a nonsolvent system was investigated using surfactant modified lipase which is a complex of lipase, Rhizopus japonicus and surfactant, sorbitan monostearate. 74% conversion of was obtained after a 48-h reaction period, and the triglyceride composition was well described by the 1, 3-random 2-random stochastic model. The transesterification reaction between MCT and LCT closely followed the simple kinetic model, and the change in MCT and LCT contents could be simulated using one parameter. The effects of the water activity (A(w)) of modified lipase, the water content of the reaction system and the reaction temperature on the reaction rate were studied. A modified lipase A(w) of 0.35 and a water content of the reaction system at 0.09 wt % showed the highest activity. Inactivation did not occur below 60 degrees C, however, the activity decreased at temperatures over 70 degrees C.     

The significance of plasma triacylglycerols in metabolism of free fatty acids and triacylglycerols in rat skeletal muscles

The continuous uptake of plasma triacylglycerols has been shown to be necessary to maintain the stable resting concentration of free fatty acids and triacylglycerols only in a muscle composed of fast--twitch oxidative glycolytic fibres.     

Structured triacylglycerol containing medium-chain fatty acids in sn-1(3) facilitates the absorption of dietary long-chain fatty acids in rats

A study was carried out to examine if the positional distribution of medium chain fatty acids (MCF) in triacylglycerol influences dietary fat absorption in rats. Two types of structure-specific fats, one predominantly composed of MCF in sn-1(3) and iinoleic acid in sn-2 [sn1(3)MCF-structured] and the others of MCF in sn-2 and linoleic acid in sn-1(3) [sn-2MCF-structured], were initially prepared, and the two structure-specific fats were interesterified and designated as sn-1(3)MCF-interesterified and sn-2MCF-interesterified. Synthetic fat was mixed with an equal amount of cocoa butter (103 g/kg of diet) and was supplemented to the AIN93G-based diet. Rats were fed on the diets for 4 wk. Long-chain saturated fatty acids were the predominant fatty acids excreted into the feces, and the positional distribution of MCF resulted in an altered fat absorption rate (%) of 81.8, 82.5, 84.2 and 86.3 for the rats fed on the diets containing sn-2MCF-structured, sn-1(3)MCF-interesterified, sn-2MCF-interesterified and sn-1(3)MCF-structured fats, respectively. The proportion of MCF in the serum, liver and adipose tissue triacylglycerols was not affected by the MCF distribution of the dietary fats. These results indicate that the distribution of MCF in dietary triacylglycerol is a determinant of intestinal fat absorption.     

Effect of fatty acid composition of dietary fat on energy balance and expenditure in hamsters

The comparative effects of feeding diets containing corn, olive, coconut, or menhaden fish oil on efficiency of energy deposition and on short term energy expenditure were examined in growing hamsters. Diets comprising oils mixed with laboratory diets at 10% oil w/w were fed ad libitum for 3 weeks. Animals fed laboratory diets were used as controls. Body composition was determined before and after the feeding period using 3H2O distribution space. Oxygen consumption was measured in each animal during the final week. Weight gains of groups fed corn and olive oil diets exceeded those of the group fed laboratory diet alone (p less than 0.05), although metabolizable energy intakes were similar across groups. Corn oil fed animals demonstrated higher carcass energy gains as fat compared with laboratory diet fed or menhaden oil fed groups. This was reflected in an increased fractional deposition of metabolizable energy intake in the group fed corn oil diet compared with the latter two groups. Fecal energy losses were lower in the group fed corn oil diet, and higher in the group fed laboratory diet alone, compared with other groups. Oxygen consumption did not differ between groups. These findings indicate that feeding dietary fish oil, compared with corn oil, favours energy substrate oxidation reducing the fraction of metabolizable energy partitioned for storage.     

Effect of glucose and long-chain fatty acids on synthesis of long-chain alcohols by Candida albicans

Candida albicans, grown aerobically in glucose-containing media, produced C14, C16 and C18 saturated long-chain alcohols only after the end of exponential growth. Contents of C14 alcohols were always lowest, and C16 and C18 alcohol contents about equal. Contents of all three classes of alcohol increased as the concentration of glucose in aerobic cultures harvested after 168 h incubation was raised from 1.0 to 30.0% (w/v). However, in 168 h anaerobic cultures, greatest long-chain alcohol contents in organisms were obtained using media containing 10% (w/v) glucose. Substituting glucose (10%, w/v) with the same concentration of galactose in aerobic cultures greatly decreased contents of long-chain alcohols, while inclusion of 10% (w/v) glycerol virtually abolished their synthesis. Supplementing anaerobic cultures with odd-chain fatty acids induced synthesis of odd-chain alcohols. Maximum conversion of fatty acid to the corresponding long-chain alcohol was observed with heptadecanoic acid. The effect of glucose on production of heptadecanol from exogenously provided heptadecanoic acid was similar to that observed on synthesis of the three major even-chain alcohols in media lacking a fatty-acid supplement. Cell-free extracts of organisms catalysed in vitro conversion of palmitoyl-CoA to 1-hexadecanol.     

High-fat diets rich in medium- versus long-chain fatty acids induce distinct patterns of tissue specific insulin resistance

Excess dietary long-chain fatty acid (LCFA) intake results in ectopic lipid accumulation and insulin resistance. Since medium-chain fatty acids (MCFA) are preferentially oxidized over LCFA, we hypothesized that diets rich in MCFA result in a lower ectopic lipid accumulation and insulin resistance compared to diets rich in LCFA. Feeding mice high-fat (HF) (45% kcal fat) diets for 8 weeks rich in triacylglycerols composed of MCFA (HFMCT) or LCFA (HFLCT) revealed a lower body weight gain in the HFMCT-fed mice. Indirect calorimetry revealed higher fat oxidation on HFMCT compared to HFLCT (0.011.0±0.0007 vs. 0.0096±0.0015 kcal/g body weight per hour, P<.05). In line with this, neutral lipid immunohistochemistry revealed significantly lower lipid storage in skeletal muscle (0.05±0.08 vs. 0.30±0.23 area%, P <.05) and in liver (0.9±0.4 vs. 6.4±0.8 area%, P<.05) after HFMCT vs. HFLCT, while ectopic fat storage in low fat (LF) was very low. Hyperinsulinemic euglycemic clamps revealed that the HFMCT and HFLCT resulted in severe whole body insulin resistance (glucose infusion rate: 53.1±6.8, 50.8±15.3 vs. 124.6±25.4 μmol min⁻¹ kg⁻¹, P<.001 in HFMCT, HFLCT and LF-fed mice, respectively). However, under hyperinsulinemic conditions, HFMCT revealed a lower endogenous glucose output (22.6±8.0 vs. 34.7±8.5 μmol min⁻¹ kg⁻¹, P<.05) and a lower peripheral glucose disappearance (75.7±7.8 vs. 93.4±12.4 μmol min⁻¹ kg⁻¹, P<.03) compared to HFLCT-fed mice. In conclusion, both HF diets induced whole body insulin resistance compared to LF. However, the HFMCT gained less weight, had less ectopic lipid accumulation, while peripheral insulin resistance was more pronounced compared to HFLCT. This suggests that HF-diets rich in medium- versus long-chain triacylglycerols induce insulin resistance via distinct mechanisms.     

Effect of methotrexate on long-chain fatty acid metabolism in liver of rats fed a standard or a defined, choline-deficient diet

The effect of methotrexate on lipids in serum and liver and key enzymes involved in esterification and oxidation of long-chain fatty acids were investigated in rats fed a standard diet and a defined choline-deficient diet. Hepatic metabolism of long-chain fatty acids were also studied in rats fed the defined diet with or without choline. When methotrexate was administered to the rats fed the standard diet there was a slight increase in hepatic lipids and a moderate reduction in the serum level. The palmitoyl-CoA synthetase activity and the microsomal glycerophosphate acyltransferase activity in the liver of rats were increased by methotrexate. The data are consistent with those where the liver may fail to transfer the newly formed triacylglycerols into the plasma with a resultant increase in liver triacylglycerol content and a decrease in serum lipid levels. Fatty liver of methotrexate-exposed rats can not be attributed simply to a reduction of fatty acid oxidation as the carnitine palmitoyltransferase activity was increased. The methotrexate response in the rats fed the defined choline-deficient diet was different. There was a reduction in both serum and hepatic triacylglycerol and the glycerophosphate acyltransferase and palmitoyl-CoA synthetase activities. The carnitine palmitoyltransferase activity was unchanged. Hepatomegaly and increased hepatic fat content, but decreased serum triacylglycerol, total cholesterol and HDL cholesterol were found to be related to the development of choline deficiency as the pleiotropic responses were almost fully prevented by addition of choline to the choline-deficient diet. Addition of choline to the choline-deficient diet normalized the total palmitoyl-CoA synthetase and carnitine palmitoyltransferase activities. In contrast to methotrexate exposure, choline deficiency increased the mitochondrial glycerophosphate acyltransferase activity. The data are consistent with those of where fatty liver induction of choline deficiency may be related to an enhanced esterification of long-chain fatty acids concomitant with a reduction of their oxidation.     

The metabolism of long-chain fatty acids and alcohols byCandida tropicalis andSaccharomyces cerevisiae

The factors affecting the growth ofCandida tropicalis andSaccharomyces cerevisiae on medium- and long-chain fatty acids and alcohols in batch culture were investigated. Growth on solid acids and alcohols dispersed in the medium is a maximum for tetradecanoic acid and tetradecanol. The poorer growth observed on shorter chain lengths can be ascribed to their toxicity to the yeasts, whilst the fall off in growth on the higher members is explained by their increasing insolubility in the medium. When the longer-chain-length acids are dissolved in a non-metabolisable hydrocarbon, the growth ofC. tropicalis is improved, but that ofS. cerevisiae is unaffected. This suggests that acids can enter the cells of the former organism by direct contact with the hydrocarbon droplets. The surface ofS. cerevisiae is too hydrophilic for this transfer mechanism to be possible. Fatty acids dissolved in gas oil are utilized as substrates for the growth ofCandida tropicalis in competition with then-paraffins contained in the gas oil. Each fatty acid contributes to a constant proportion of yeast produced, but this proportion decreases as the chain is lengthened. Thus, in mixtures of gas oil with dodecanoic acid, 65% of the yeast is produced from metabolism of the acid, while with octadecanoic acid only 15% is produced. The log specific rates of utilization of the fatty acids within this range diminish linearly with increasing chain length.     

Membrane lipid biosynthesis in Acholeplasma laidlawii b: elongation of medium- and long-chain exogenous fatty acids in growing cells

The chain elongation of a wide variety of exogenous fatty acids and the subsequent incorporation of the chain elongation products into the total membrane lipids of Acholeplasma laidlawii B were systematically studied. Within each chemical class of fatty acids examined, the extent of chain elongation increased with increases in chain length, reached a maximum value, and then declined with further increases in chain length. Depending on chemical structure, exogenous fatty acids containing less than 6 to 9 carbon atoms or more than 15 to 18 carbon atoms were not substrates for the chain elongation system. The substrate specificity of this fatty acid elongation system was strikingly broad, and straight-chain, methyl isobranched, and methyl anteisobranched saturated fatty acids, as well as cis- and trans-monounsaturated, cis-cyclopropane, and cis-polyunsaturated fatty acids, underwent chain elongation in vivo. The extent of chain elongation and the average chain length of the primary elongation products correlated well with the physical properties (melting temperatures) of the exogenous fatty acid substrates. The specificity of fatty acid chain elongation in A. laidlawii B maintained the fluidity and physical state of the membrane lipids within a rather wide but definitely limited range. The fatty acid chain elongation system of this organism could be markedly influenced by the presence of a second exogenous fatty acid that was not itself a substrate for the chain elongation system but was incorporated directly into the membrane lipids. The presence of a relatively low-melting exogenous fatty acid increased both the extent of chain elongation and the average chain length of the elongation products generated, whereas the presence of a relatively high-melting fatty acid had the opposite effect. The extent of chain elongation and nature of the elongation products formed were not, however, dependent on the fluidity and physical state of the membrane lipids per se. The second exogenous fatty acid appeared instead to exert its characteristic effect by competing with the chain elongation substrate and elongation products for the stereospecific acylation of positions 1 and 2 of sn-glycerol-3-phosphate. The similar effects of alterations in environmental temperature, cholesterol content, and exposure to the antibiotic cerulenin on the fatty acid chain elongation and de novo biosynthetic activities suggested that the chain elongation system of this organism may be a component of the de novo biosynthetic system.     

Fat metabolism in higher plants: The effect of cerulenin on the synthesis of medium- and long-chain acids in leaf tissue

Addition of cerulenin to the incubation medium severely inhibited fatty acid biosynthesis in leaf tissue, chloroplasts and stromal preparations. Simultaneous with this overall inhibition, formation of medium-chain acids (C₈-C₁₂) was greatly enhanced, while increasing cerulenin concentrations favored synthesis of the shorter chain-length acids. This was ascribed to the binding of cerulenin to β-ketoacyl-ACP synthetase during the incubation which prevented further condensation and caused the release of the saturated acyl group thus formed.The proportion of linoleate synthesized in all the leaf tissues examined increased as a response to treatment with cerulenin, apparently at the expense of oleate. Cerulenin did not modify the mechanisms of synthesis of the C₁₈ unsaturated acids. The fragmentation patterns obtained after reductive ozonolysis of the material derived from the treated groups were similar in all cases to those obtained from the controls.