Comparison of catabolism rate of fatty acids to carbon dioxide in mice

The catabolism rates of a medium chain fatty acid (octanoic acid), an even‐numbered fatty acid (palmitic acid), and odd‐numbered fatty acids (pentadecanoic acid and heptadecanoic acid) in mice were compared using stable isotope (¹³C) labeled fatty acids and isotope‐ratio MS (IRMS). The catabolism rates of respective fatty acids were evaluated by the ratio of ¹³C and ¹²C in carbon dioxide expired from mice. The results show that the catabolism rate of octanoic acid is three times faster than that of palmitic acid. This result is in agreement with previous knowledge that medium chain fatty acids are easily beta‐oxidized as compared to long chain fatty acids. The catabolism rates of odd‐numbered fatty acids such as pentadecanoic acid and heptadecanoic acid were significantly lower as compared to those of even‐numbered fatty acids such as palmitic acid. This finding supports our previous report that odd‐numbered fatty acids are easily accumulated into body fat. The high accumulation of odd‐numbered fatty acids in body fat would be a direct result of their low beta‐oxidizability. Practical applications: ¹³C‐labeled fatty acids were administered to mice and the rates of ¹³CO₂ formation were compared among medium chain, even‐numbered, and odd‐numbered fatty acids using IRMS. We found that the catabolism rates of odd‐numbered fatty acids such as pentadecanoic acid and heptadecanoic acid were significantly lower in comparison to those of even‐numbered fatty acids such as palmitic acid. These findings could be valuable for the development of the lipid metabolism field.     

Metabolism of brain glycolipid fatty acids

The metabolism of the fatty acid moieties of brain cerebrosides, sulfatides, and gangliosides is reviewed and discussed. The methodology involved in the isolation of the fatty acids is described briefly. It seems clear now that most of these acids are made by chain elongation of intermediate length fatty acids by addition of acetate residues. The unsaturated acids are made by desaturation of the intermediate length acids (palmitic, heptadecanoic, stearic) followed by chain elongation. The hydroxy acids are made directly from the corresponding nonhydroxy acids, saturated, unsaturated, and odd-numbered. All the hydroxy acids undergo oxidative decarboxylation to yield fatty acids containing one less carbon atom. The odd-numbered acids are also made from propionate, which is elongated to intermediate length acids and then to longer acids. The major intermediate length “primer” acid seems to be palmitate, but there is evidence that the stearate used for cerebroside synthesis is also madede novo from acetate. The ganglioside fatty acids were found to turn over somewhat faster than the other fatty acids. Two metabolic pools for the cerebroside acids were found, one with a very high turnover rate, the other with a very low turnover rate. Presented at the Prof. Ernst Klenk Symposium on Glycolipids and the Nervous System, AOCS meeting, Houston, April 1965.     

Comparison of catabolic rates of fatty acids using stable isotope and isotope‐ratio mass spectrometry

The catabolic rates of individual fatty acids in mice were compared using stable isotope (¹³C)‐labeled fatty acids and isotope‐ratio mass spectrometry (IRMS). The catabolic rates were evaluated from the ratio of ¹³C and ¹²C in carbon dioxide expired by mice. The results showed that the catabolic rate of octanoic acid is three times faster than that of palmitic acid. This result is consistent with previous reports using radioisotope ¹⁴C showing that medium‐chain fatty acids are more easily beta‐oxidized than long‐chain fatty acids. The catabolic rates of odd‐numbered fatty acids such as pentadecanoic acid and heptadecanoic acid were significantly lower compared to those of even‐numbered fatty acids such as palmitic acid. These findings support previous reports that show odd‐numbered fatty acids easily accumulating in body fat. The high accumulation of odd‐numbered fatty acids in body fat thus directly reflects a low degree of beta‐oxidization. The combination of stable isotope‐labeled compounds and IRMS serves as a powerful tool in lipid analysis.     

Some monomethyl-branched fatty acids from ruminant fats: Open-tubular GLC separations and indications of substitution on even-numbered carbon

Isomeric methyl esters of fatty acids in three groups (C₁₅, C₁₇, C₁₉) have been isolated from ruminant fats. Basic structural analysis by physiochemical techniques indicated that these odd-numbered fatty acids were even chain with a single methyl branch on the chain. High resolution open-tubular gas liquid chromatographic studies indicate that, with the exception of iso acid impurities in these fractions, only even-numbered carbons of the fatty acid chains bear the methyl branch.     

Digestion and absorption of free and esterified fish oil fatty acids in rats

This study was designed to test the hypotheses that digestibility and post-absorption metabolism of fish oil are influenced by impaired lipolysis and by the stereospecific composition of its triacylglycerols. Male Wistar rats were fed nonpurified diets containing one of the following fat sources: 9% native fish oil (NFO), 9% autorandomized fish oil (RFO), 8.1% fish oil-derived free fatty acids (FO-FFA) plus 0.9% glycerol, or 9% soybean oil (SO) as a reference fat. In a 24-day balance study, apparent digestibility of total dietary fat averaged 93.1% in the SO, NFO and RFO groups, and 90.9% in the FO-FFA group. Randomization of fish oil had no effect on apparent digestibility of individual fatty acids. In rats fed FO-FFA, apparent absorption of saturated and monounsaturated fatty acids was lower when compared to the NFO and RFO groups. Feeding the FO-FFA diet tended to increase plasma triglyceride content. The hypocholesterolemic effect of polyunsaturated n−3 fatty acids was not influenced by the dietary source. Similar effects on fatty acid profiles of plasma and liver phospholipids were caused by the NFO, RFO and the FO-FFA diets. We conclude that once polyunsaturated n−3 fatty acids are absorbed, their effect on lipid metabolism is not determined by the dietary source.     

Effects of perfluorodecanoic acid onde novo fatty acid and cholesterol synthesis in the rat

Perfluorodecanoic acid (PFDA) is a peroxisome proliferator that causes a dose-dependent (20–80 mg/kg) increase in hepatic triacylglycerol and cholesteryl ester levels in the rat. We hypothesized that PFDA may cause an increase in thede novo synthesis of fatty acids and cholesterol in this species, which would explain observed effects. The incorporation of³H₂O into tissue lipids was examined 7 days after rats received vehicle or 20 or 80 mg/kg of PFDA. PFDA treatment decreased the rate of synthesis of cholesterol and fatty acids in the liver and in epididymal fat pad. At a PFDA dose (20 mg/kg) that decreasedde novo synthesis of fatty acids and cholesterol, there was no effect on the concentration of fatty acids and cholesterol in the liver, epididymal fat pads, and plasma. We conclude that PFDA induced fatty liver is due to either a decrease in the oxidation of fatty acids in the liver, or an impairment of triacylglycerol catabolism and/or export from the liver, and is not the result of an increase inde novo synthesis of fatty acids and cholesterol.     

The structure of polyenoic odd- and even-numbered fatty acids of mullet (Mugil cephalus)

Mullet oil contains more than 25% straight-chain odd-numbered fatty acids. Odd- and even-numbered components of chain lengths C₁₅ to C₂₀ were isolated and their structures determined. The vinylmethane rhythm prevails in all polyun-saturated acids. Numerous homologs have their double bonds in identical positions, relative to the carboxyl group, as for example, 舥^9,12- and 舥^6,9,12-C₁₅, -C₁₆, -C₁₇ and -C₁₈ acids. The terminal structures which are characteristic for oleic, linoleic, etc., families are not found in the unsaturated odd-numbered acids. The results show: that the proximal structure has greater influence than the terminal structure on the biosynthesis of unsaturated odd-numbered acids; that chain lengths of 17 and 18 carbon atoms with double bonds in position 9 are crucial for synthesis of the polyenoic C₁₉ and C₂₀ acids; that chain lengths C₁₅ and C₁₆ with double bonds in position 9 are suitable for desaturation but that they are not suitable for desaturation after elongation. These specifications bring all acids of mullet into a rational order and reflect their possible interconversions. Presently, such classification has only limited predictive value in regard to the physiological properties of polyunsaturated acids. However, the new definitions for grouping the polyunsaturated fatty acids lead to interesting working hypotheses.     

The deposition of polyunsaturated fatty acids in the rat fed partially hydrogenated vegetable oil

The composition of deposited polyenoic fatty acids in rats fed liquid or partially hydrogenated corn oil was determined by gas chromatography, which did not distinguish isomeric forms, and by lipoxidase which reacted with thecis, cis-methylene-interrupted acids. The two methods gave similar results for the liver fatty acids of rats fed either the unhydrogenated or partially hydrogenated oil. Of the fatty acids from the epididymal fat pads of rats fed the hydrogenated product, an appreciable quantity of linoleate isomers did not react with lipoxidase. The total amount of linoleic acid deposited was related to the total fatty acid pattern of the dietary oil. It appeared that thetrans-acids were mostly metab-olized and that the originalcis,cis-linoleic acid remaining in the partially hydrogenated product was preferentially incorporated into tissues. One of 10 papers to be published from the Symposium “Hydrogenation” presented at the AOCS Meeting, New Orleans, April 1970.     

Hepatic metabolism of 1-14C octanoic and 1-14C palmitic acids

The hepatic metabolism of 1⁻¹⁴C octanoic acid was compared with that of 1⁻¹⁴C palmitic acid in male rats which were fed. After intraportal injection only 1/6 to 1/18 as much octanoic acid as palmitic acid was incorporated into hepatic lipids. In contrast, octanoic acid yielded two to four times as much water-soluble product as did palmitic acid. Similar, but even more impressive, differences between the incorporation of these fatty acids into hepatic lipids were observed in liver slices incubated with¹⁴C octanoate and¹⁴C palmitate. The oxidation of octanoate to CO₂ was more than 10 times as great as that of palmitate. With both substrates, triglycerides comprised almost half the labeled lipid recovered. However octanoate yielded a higher proportion of labeled, unesterified fatty acids and a lower proportion of labeled phospholipid and monoglycerides than did palmitate. Most of the¹⁴C recovered in hepatic lipids after incubation with 1⁻¹⁴C octanoate was found in the carboxyl groups of long-chain fatty acids, suggesting that the latter had been synthesized from 2-carbon fragments formed from the oxidation of octanoate. In contrast, only a small fraction of the palmitate was elongated. The similarities and differences between the metabolism of octanoic and palmitic acid in liver and intestine, and the possible nutritional significance of octanoic acid are discussed.     

Different metabolism of saturated and unsaturated long chain plasma free fatty acids by intestinal mucosa of rats

During fat absorption, unsaturated long chain fatty acids are esterified at a higher rate than saturated fatty acids of similar chain length. This phenomenon has been attributed to differences in the binding affinity of fatty acids to a cytosolic fatty acid-binding protein. As intestinal mucosa utilizes plasma free fatty acids as well, we investigated whether long chainplasma free fatty acids of different degree of saturation are metabolized also at different rates.³H-Palmitic and¹⁴C-linoleic acid complexed to rat serum were injected rapidly into a tail vein of fasting rats. One, 2 and 4 min later there was no difference between³H and¹⁴C-radioactivity in intestinal mucosa, suggesting equal initial uptake of the two labeled fatty acids from plasma. Despite their equal uptake, the incorporation of the isotopes into ester lipids was significantly different, however: at 2 min, 53.1±3.9% of³H and 73.8±4.6% of¹⁴C were recovered in ester lipids. Phospholipids and triglycerides accounted for most of the mucosal³H and¹⁴C. At 4 min, a similar distribution of isotopes in intestinal mucosal metabolites was found. These data show that despite equal initial uptake by intestinal mucosa unsaturated long chain fatty acids taken up from plasma are esterified to a higher and oxidized to a lower extent than saturated plasma free fatty acids. Unsaturated plasma free fatty acids, therefore, may provide a more important source of fatty acids for endogenous intestinal lipoprotein lipids than saturated plasma free fatty acids. It is speculated that the fatty acid binding protein might be operative not only in the intracellular transport and metabolism of luminal fatty acids but of plasma free fatty acids as well.     

Metabolism of trans fatty acids by hepatocytes

The present work was undertaken to study the metabolism of fatty acids with trans double bonds by rat hepatocytes. In liver mitochondria, elaidoyl-CoA was a poorer substrate for carnitine palmitoyltransferase I (CPT-I) than oleoyl-CoA. Likewise, incubation, of hepatocytes with oleic acid produced a more pronounced stimulation of CPT-I than incubation with trans fatty acids. This was not due to a differential effect of cis and trans fatty acids on acetyl-CoA carboxylase (ACC) activity and malonyl-CoA levels. Elaidic acid was metabolized by hepatocytes at a higher rate than oleic acid. Surprisingly, compared to oleic acid, elaidic acid was a better substrate for mitochondrial and, especially, peroxisomal oxidation, but a poorer substrate for cellular and very low density lipoprotein triacylglycerol synthesis. Results thus show that trans fatty acids are preferentially oxidized by hepatic peroxisomes, and that the ACC/malonyl-CoA/CPT-I system for coordinate control of fatty acid metabolism is not responsible for the distinct hepatic utilization of cis and trans fatty acids.     

Effect of dietarytrans fatty acids on microsomal enzymes and membranes

Three groups of rats were maintained on diets containing different proportions oftrans fatty acids (0, 18.3 or 36.6% of the total fatty acids) for eight weeks. No differences in body weight were observed among the three groups, but the fat cell size, determined in epididymal fat, differed significantly between the controls and the rats fed diets containingtrans fatty acids. The supernatant obtained by centrifuging homogenates of liver from the rats at 9000×g (S-9 fraction) was used as an activator in a bacterial test for mutagenicity of 2-aminofluorene and aflatoxin B₁ usingSalmonella typhimurium strains TA 98 and TA 100, respectively. The mutagenicities of 2-aminofluorene in strain TA 98 and of aflatoxin B₁ in strain TA 100 were significantly lower with the liver S-9 fraction from rats fed a diet containing 36.6%trans fatty acids than with the liver S-9 fraction from rats fed a control diet with notrans fatty acids.     

Effect of high fat corn oil,olive oil and fish oil on phospholipid fatty acid composition in male F344 rats

Epidemiological and laboratory animal model studies have provided evidence that the effect of dietary fat on colon tumorigenesis depends on the amount of fat and its composition. Because of the importance of the composition of dietary fat and of tissue membrane fatty acid composition in tumor promotion, experiments were designed to investigate the relative effects of high fat diets rich in ω3, ω6 and ω9 fatty acids and colon carcinogen on the phospholipid fatty acid composition of liver, colon, small intestine, erythrocytes and blood plasma. At 6 wk of age, groups of animals were fed diets containing 5% corn oil (LFCO), 23.5% corn oil (HFCO), 23.5% olive oil (HFOO), and 20.5% fish oil plus 3% corn oil (HFFO). Two weeks later all the animals except the vehicle-treated animals received azoxymethanes.c. once weekly for 2 wk at a dose rate of 15 mg/kg body weight. Animals were sacrificed 5 d later and liver, colon, small intestine and erythrocytes and blood plasma were analyzed for phospholipid fatty acids. The results indicate that the phospholipid fatty acid composition of liver, colon and small intestine of HFCO diet fed animals, were not significantly different from those fed the LFCO diet. The levels of palmitoleic acid and linoleic acid were increased in erythrocytes and blood plasma of the animals fed the HFCO diet compared to those fed the LFCO diet. Feeding the HFCO diet significantly increased the oleic acid content and decreased the linoleic acid and arachidonic acid levels in various organs when compared to the HFCO diet. Animals fed the HFFO diet showed a marked increase in eicosapentaenoic acid and docosahexaenoic acid and a decrease in linoleic acid and arachidonic acid levels as compared to those fed the HFCO diet. The results also indicate that carcinogen treatment had only a minimal effect on the phospholipid fatty acid composition.     

The absorption of fatty acids by functional bovine mammary cells

Freshly dispersed bovine mammary cells rapidly absorbed long chain fatty acids from the culture medium. Differences in the rates of absorption were observed, i.e., palmitic > stearic > oleic > myristic > linoleic acid. The preponderance of the fatty acids absorbed were esterified into triglycerides (>75%) and the remainder were mostly incorporated into phospholipids. The cells secreted triglycerides into the culture medium. Of the phospholipid classes, phosphatidylcholine always contained most of the radioactivity in all experiments with labeled fatty acids. These observations are related to the metabolism of mammary cells in vivo.     

Comparison of body weight and adipose tissue in male C57BI/6J mice fed diets with and withouttrans fatty acids

The effect of a diet containingtrans-fatty acids (tFA) on the fatty acid composition and fat accumulation in adipose tissue was investigated in mice. Male C57BI/6J mice were fed Control or Trans Diets that were similar, except that 50% of the 18∶1, which was allcis in the Control Diet, was replaced bytFA in the Trans Diet. At selected ages, body weight, epididymal fat pad weight, perirenal fat yield, adipose tissue cellularity and fatty acid composition were examined. Over the time period studied (2–24 mon), the proportion of 18∶0 and 16∶0 tended to decrease whilecis-18∶1 levels increased. Compared to the Control Diet, the Trans Diet resulted in adipose tissue lipids with higher percentages of 14∶0 and 18∶2n−6 and lower percentages ofcis-18∶1 and 20∶4n−6. In polar lipids,tFA replaced saturated fatty acids, whereastFA replacedcis-18∶1 in the nonpolar lipids. Body weights at 16 and 24 mon of age and epididymal fat pad weights at 8–24 mon of age were lower in mice fed the Trans Diet as compared to those fed the Control Diet. At the ages studied, the Trans Diet also resulted in lower values for perirenal fat weights, triacylglycerol to polar lipid ratios, and adipose cell size. The data suggest that chronic consumption oftFA affects lipid metabolism and results in decreased fat accumulation in murine adipose tissue.     

Surface shear viscosity of straight chain (c15 to c20) fatty acids

Experiments were carried out to measure surface shear viscosities of a series of straight chain fatty acids from C₁₅ to C₂₀. The experimental results indicated that members of the series with even-numbered C-atoms were essentially surface-Newtonian in behaviour with viscosity increasing with increasing chain length. However, members of the series with odd-numbered C-atoms were surface pseudoplastic and the degree of pseudo-plasticity decreased with increase in chain length. The experimental results also indicated that aging of surface-active solutions increases their surface shear viscosities.     

Effects of protected cyclopropene fatty acids on the composition of ruminant milk fat

Unsaturated fatty acids can be protected from ruminal hydrogenation, and, when fed to lactating ruminants, the constituent acids are incorporated into milk triacylglycerols. By this means, it has been possible to reduce the melting point of milk triglycerides and to make softer butter fat. This report shows that, by feeding small amounts of protected cyclopropene fatty acids, one is also able to make harder butter fat.Sterculia foetida seed oil, a rich source of cyclopropene fatty acids, was emulsified with casein and spray dried to yield a free flowing dry powder. When this material was treated with formaldehyde and fed to lactating goats (ca. 1 g cyclopropene fatty acids per day), there were substantial increases in the proportions of stearic acid and decreases in the proportions of oleic acid in milk fat. Similar results were obtained when the formaldehyde-treated supplements were fed to lactating cows (ca. 3 g cyclopropene fatty acids per day). The effect was considerably less apparent when theS. foetida seed oilcasein supplement was not treated with formaldehyde, suggesting that cyclopropene fatty acids are hydrogenated in the rumen as are other unsaturated fatty acids. The effect of feeding protected cyclopropene fatty acids on the stearic: oleic ratio in milk fat is probably due to cyclopropene-mediated inhibition of the mammary desaturase enzymes.     

Elongation and desaturation of dietary fatty acids in turbotScophthalmus maximus L., and rainbow trout,Salmo gairdnerii rich

Turbot and rainbow trout, which had previously recieved diets free of fat, were fed [1-14C] fatty acids. The distribution of radioactivity in the tissue fatty acids was examined 6 days later. In rainbow trout fed [1-14C] 18:3omega3, 70% of the radioactivity was present in 22:6omega3 fatty acid. In contrast, turbot fed [1-14C] 18:1omega9, 18:2omega6, or 18:3omega3 converted only small amounts of labeled fatty acids (3-15%) into fatty acids of longer chain length. The major product of the limited modification found in turbot was the dietary acid elongated by 2 carbon atoms.     

The influence of dietary nucleotides and long-chain polyunsaturated fatty acids on the incorporation of [3H] arachidonic acid on experimental liver cirrhosis

The purposes of this study were to determine: a) the incorporation of labeled [3H] arachidonic acid on the intestinal mucosa, the liver and plasma, after 1,3 and 5 hours of administration, b) preferential incorporation by different tissues, c) and the effects on experimental rats with thioacetamide-induced cirrhosis, after four weeks of a dietary supplementation with nucleotides and long-chain polyunsaturated fatty acids. 209 female Wistar rats were divided into two groups (control and TAA group). The TAA group was given 300 mg of thioacetamide/L, in their drinking water for four months. After this period, a sample of 6 rats were taken from each group and examined, to evaluate the biochemical and histological changes of the experimental model, and 36 rats were taken to determine the incorporation of radioactivity by the groups. The rest of the animals were divided into four subgroups. Each group, receiving a supplementary diet with only long-chain polyunsaturated fatty acids and/or nucleotides or neither, for 4 weeks. After four months of thioacetamide, the incorporation of the [3H] arachidonic acid showed: a) an increased within 3 h in the intestinal mucosa, b) a decreased in the liver after 3 to 5 h c) and a drastic decrease in the plasma after 3 to 5 h. With a dietary supplementation of long-chain polyunsaturated fatty acids and nucleotides combined, there was a decrease of accumulate [3H] arachidonic acid in the intestine and a increase in the liver and plasma. The simultaneous supply of dietary polyunsaturated fatty acids and nucleotides was beneficial in the reversal of abnormalities of the lipid metabolism, in this experimental model of liver cirrhosis.     

Influence of moderate amounts of trans fatty acids on the formation of polyunsaturated fatty acids

The effect of trans fatty acids from partially hydrogenated soybean oil and butterfat on the formation of polyunsaturated fatty acids was investigated. Five groups of rats were fed diets that contained 20 wt% fat. The content of linoleic acid was adjusted to 10 wt% of the dietary fats in all diets, whereas the amount of trans fatty acids from partially hydrogenated soybean oil (PHSBO) was varied from 4.5 to 15 wt% in three of the five diets. The fourth group received trans fatty acids from butterfat (BF), while the control group was fed palm oil without trans fatty acids. Trans fatty acids in the diet were portionally reflected in rat liver and heart phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylinositol, and phosphatidylserine. Incorporation in the sn-1 position was compensated by a decrease in saturated fatty acids. Trans fatty acids were not detected in diphosphatidylglycerol. Compared to the presence in the dietary fats, 8t- and 10t-18:1 were discriminated against in the incorporation in PE and PC from liver and heart, whereas 9t- and 12t-18:1 were preferred. The formation of 20:4n-6 was not influenced by 4.5 wt% trans fatty acids (from PHSBO) but apparently was by 10 wt% in liver. In contrast, even a content of 2.5 wt% trans fatty acids from BF reduced the formation of 20:4n-6. The inhibitory effect of trans isomers on linoleic acid conversion was reflected less in heart than in liver and less for PE than for PC. Groups with trans fatty acids showed increased 22:6n-3 and 22:5n-3 deposition in liver and heart PE and PC.