Distribution of isomeric octadecenoic fatty acids in milk fat

Suppression of amyloid-β secretion from neurons by cis-9, trans-11-octadecadienoic acid, an isomer of conjugated linoleic acid

Two common conjugated linoleic acids (LAs), cis-9, trans-11 CLA (c9,t11 CLA) and trans-10, cis-12 CLA (t10,c12 CLA), exert various biological activities. However, the effect of CLA on the generation of neurotoxic amyloid-β (Aβ) protein remains unclear. We found that c9,t11 CLA significantly suppressed the generation of Aβ in mouse neurons. CLA treatment did not affect the level of β-site APP-cleaving enzyme 1 (BACE1), a component of active γ-secretase complex presenilin 1 amino-terminal fragment, or Aβ protein precursor (APP) in cultured neurons. BACE1 and γ-secretase activities were not directly affected by c9,t11 CLA. Localization of BACE1 and APP in early endosomes increased in neurons treated with c9,t11 CLA; concomitantly, the localization of both proteins was reduced in late endosomes, the predominant site of APP cleavage by BACE1. The level of CLA-containing phosphatidylcholine (CLA-PC) increased dramatically in neurons incubated with CLA. Incorporation of phospholipids containing c9,t11 CLA, but not t10,c12 CLA, into the membrane may affect the localization of some membrane-associated proteins in intracellular membrane compartments. Thus, in neurons treated with c9,t11 CLA, reduced colocalization of APP with BACE1 in late endosomes may decrease APP cleavage by BACE1 and subsequent Aβ generation. Our findings suggest that accumulation of c9,t11 CLA-PC/LPC in neuronal membranes suppresses production of neurotoxic Aβ in neurons.

Conjugated Linoleic Acid Effects on Cancer, Obesity, and Atherosclerosis: A Review of Pre-Clinical and Human Trials with Current Perspectives

Obesity and its comorbidities, including type 2 diabetes and cardiovascular disease, are straining our healthcare system, necessitating the development of novel strategies for weight loss. Lifestyle modifications, such as exercise and caloric restriction, have proven effective against obesity in the short term, yet obesity persists because of the high predilection for weight regain. Therefore, alternative approaches to achieve long term sustainable weight loss are urgently needed. Conjugated linoleic acid (CLA), a fatty acid found naturally in ruminant animal food products, has been identified as a potential anti-obesogenic agent, with substantial efficacy in mice, and modest efficacy in obese human populations. Originally described as an anti-carcinogenic fatty acid, in addition to its anti-obesogenic effects, CLA has now been shown to possess anti-atherosclerotic properties. This review summarizes the pre-clinical and human studies conducted using CLA to date, which collectively suggest that CLA has efficacy against cancer, obesity, and atherosclerosis. In addition, the potential mechanisms for the many integrative physiological effects of CLA supplementation will be discussed in detail, including an introduction to the gut microbiota as a potential mediator of CLA effects on obesity and atherosclerosis.

Trans-octadecenoic Acid Positional Isomers Have Different Accumulation and Catabolism Properties in Mice

Trans fatty acids (TFA) are considered risk factors for cardiovascular disease (CVD), while the details of distribution and metabolism of the individual isomers are not clear. Here we investigated the accumulation and catabolic rate of TFA positional isomers of octadecenoic acid (18:1) in mice. ICR mice were fed deuterium- and [1-(13)C] stable isotope-labeled trans-9-18:1 (9t-18:1*), trans-10-18:1 (10t-18:1*), or trans-11-18:1 (11t-18:1*) for 2 or 4 weeks, or a TFA mixture (9t-18:1*, 10t-18:1*, and 11t-18:1*) for 3 weeks. Analysis of whole-body tissues by gas chromatography-chemical ionization mass spectrometry revealed the highest 9t-18:1* levels in the heart. Significant differences in the accumulation of the respective trans-18:1 were observed in the heart and erythrocytes, where 9t- > 11t- > 10t-18:1*, but no significant difference was observed in the liver or white adipose tissue (WAT). Mice fed on 11t-18:1 demonstrated accumulation of endogenously synthesized conjugated linoleic acid in the liver, WAT, and heart, but any other metabolites were not found in other groups. Furthermore, we analyzed catabolic rates of single-dose-administered trans-18:1* isomers into [(13)C]-labeled CO2 using isotope-ratio mass spectrometry, and the 10t-18:1*catabolic rate was significantly higher than those of 9t- and 11t-18:1*. We found that the accumulation and catabolism of trans-18:1 positional isomers varied in these mice. Differential accumulation in tissues suggests that individual TFA positional isomers may play different roles in human health.

The effects of changing dairy intake on trans and saturated fatty acid levels- results from a randomized controlled study

Background

Dairy food is an important natural source of saturated and trans fatty acids in the human diet. This study evaluates the effect of dietary advice to change dairy food intake on plasma fatty acid levels known to be present in milk in healthy volunteers.

Methods

Twenty one samples of whole fat dairy milk were analyzed for fatty acids levels. Changes in levels of plasma phospholipid levels were evaluated in 180 healthy volunteers randomized to increase, not change or reduce dairy intake for one month. Fatty acids were measured by gas chromatography–mass spectrometry and levels are normalized to d-4 alanine.

Results

The long chain fatty acids palmitic (13.4%), stearic (16.7%) and myristic (18.9%) acid were most common saturated fats in milk. Four trans fatty acids constituted 3.7% of the total milk fat content. Increased dairy food intake by 3.0 (± 1.2) serves/ day for 1 month was associated with small increases in plasma levels of myristic (+0.05, 95% confidence level-0.08 to 0.13, p = 0.07), pentadecanoic (+0.014, 95% confidence level -0.016 to 0.048, p = 0.02) and margaric acid (+0.02, -0.03 to 0.05, p = 0.03). There was no significant change in plasma levels of 4 saturated, 4 trans and 10 unsaturated fatty acids. Decreasing dairy food intake by 2.5 (± 1.2) serves per day was not associated with change in levels of any plasma fatty acid levels.

Conclusion

Dietary advice to change dairy food has a minor effect on plasma fatty acid levels.

Trial registration

ACTRN12612000574842.

Subcutaneous and intramuscular adipose tissue stearoyl-coenzyme A desaturase gene expression and fatty acid composition in calf- and yearling-fed Angus steers

We proposed that stearoyl-CoA desaturase (SCD) activity dictates fatty acid composition of adipose tissue and muscle in beef cattle, regardless of ruminal or hepatic fatty acid hydrogenation or desaturation. Twelve Angus steers were assigned to a calf-fed (CF) group and slaughtered at weaning (8 mo of age; n=4), 12 mo of age (n=4), or 16 mo of age (n=4). Twelve steers were assigned to a yearling-fed (YF) group and slaughtered at 12 mo of age (n=4), 16 mo of age (n=4), and 17.5 mo of age (n=4; 525 kg, market weight). Data were analyzed based on time on the corn-based finishing diet, with terminal age as a covariate, and orthogonal polynomial contrasts were tested on the main effects of treatment group and time on the finishing diet. Fatty acids from duodenal digesta, plasma, liver, LM, and subcutaneous and intramuscular adipose tissue were measured, and SCD gene expression was measured in intramuscular and subcutaneous adipose tissues. In duodenal digesta, palmitic and linoleic acids increased by 100% over the sampling period, α-linolenic acid decreased over the sampling period, and trans-vaccenic acid was greater in YF than in CF steers (all P < 0.01). The proportion of α-linolenic acid decreased over time in all tissues, including liver. The SCD index (ratio of SCD fatty acid products to SCD fatty acid substrates) increased over time in LM and in intramuscular and subcutaneous adipose tissues. The SCD:glyceraldehyde 3-phosphate dehydrogenase mRNA ratio was virtually undetectable at the initial sampling periods in subcutaneous adipose tissue of YF and CF steers, and it increased over time (P < 0.01). The SCD index and SCD:glyceraldehyde 3-phosphate dehydrogenase ratio were greater in intramuscular adipose tissue of CF steers than in that of YF steers. The SCD index did not change over time in liver and decreased over time in duodenal digesta. We conclude that, unlike essential fatty acids, the SFA and MUFA composition of adipose tissue is regulated by adipose tissue fatty acid desaturation, with little contribution from hepatic or duodenal fatty acids.

Pilot study on the effects of dietary conjugated linoleic acid on tumorigenesis and gene expression in PyMT transgenic mice

Conjugated linoleic acid (CLA) is a class of commercially available fatty acids that have been associated with anticancer properties in rodent models of chemical carcinogenesis. We conducted a pilot study to examine the antitumor effect of dietary CLA in a polyoma virus-middle T antigen (PyMT) mouse model of invasive breast cancer. Virgin 4-week-old PyMT mice were administered a mixed-isomer CLA diet (1% wt/wt) or control AIN-93G diet for 4 weeks (N = 6 and 5, respectively) and tumor burden was assessed at 8 weeks of age. Thoracic mammary glands were prepared as whole mounts with other glands being formalin fixed and paraffin embedded for histology and immunohistochemistry (IHC). Total RNA was prepared for microarray and real-time reverse transcription-polymerase chain reaction analysis. Western blots were performed for protein expression analysis. Tumor incidence was significantly increased in CLA-treated animals compared with controls (P = 0.009) and occurred with extensive lobular-alveolar expansion and loss of mammary adipose tissue. More than 100 genes were downregulated > or = 2-fold in the CLA-treated group compared with controls, including adipose-specific markers, as wells as cytoskeletal and adhesion-related genes. This was supported by dramatic decreases in the epithelial adherens E-cadherin and beta-catenin as demonstrated by IHC. Taken together, these results suggest that dietary CLA affects the mammary stromal environment, leading to tumor progression and cellular expansion in the PyMT mouse model. Further studies of the potential for cancer promotion are needed, especially because mixed-isomer CLA formulations are sold commercially as a nutritional supplement.

Effect of animal and industrial trans fatty acids on HDL and LDL cholesterol levels in humans--a quantitative review

BACKGROUND

Trans fatty acids are produced either by industrial hydrogenation or by biohydrogenation in the rumens of cows and sheep. Industrial trans fatty acids lower HDL cholesterol, raise LDL cholesterol, and increase the risk of coronary heart disease. The effects of conjugated linoleic acid and trans fatty acids from ruminant animals are less clear. We reviewed the literature, estimated the effects trans fatty acids from ruminant sources and of conjugated trans linoleic acid (CLA) on blood lipoproteins, and compared these with industrial trans fatty acids.

METHODOLOGY/PRINCIPAL FINDINGS

We searched Medline and scanned reference lists for intervention trials that reported effects of industrial trans fatty acids, ruminant trans fatty acids or conjugated linoleic acid on LDL and HDL cholesterol in humans. The 39 studies that met our criteria provided results of 29 treatments with industrial trans fatty acids, 6 with ruminant trans fatty acids and 17 with CLA. Control treatments differed between studies; to enable comparison between studies we recalculated for each study what the effect of trans fatty acids on lipoprotein would be if they isocalorically replaced cis mono unsaturated fatty acids. In linear regression analysis the plasma LDL to HDL cholesterol ratio increased by 0.055 (95%CI 0.044-0.066) for each % of dietary energy from industrial trans fatty acids replacing cis monounsaturated fatty acids The increase in the LDL to HDL ratio for each % of energy was 0.038 (95%CI 0.012-0.065) for ruminant trans fatty acids, and 0.043 (95% CI 0.012-0.074) for conjugated linoleic acid (p = 0.99 for difference between CLA and industrial trans fatty acids; p = 0.37 for ruminant versus industrial trans fatty acids).

CONCLUSIONS/SIGNIFICANCE

Published data suggest that all fatty acids with a double bond in the trans configuration raise the ratio of plasma LDL to HDL cholesterol.

High dietary consumption of trans fatty acids decreases brain docosahexaenoic acid but does not alter amyloid-beta and tau pathologies in the 3xTg-AD model of Alzheimer's disease

Dietary consumption of trans fatty acids (TFA) has increased during the 20th century and is a suspected risk factor for cardiovascular diseases. More recently, high TFA intake has been associated with a higher risk of developing Alzheimer's disease (AD). To investigate the impact of TFA on an animal model genetically programmed to express amyloid-beta (Abeta) and tau pathological markers of AD, we have fed 3xTg-AD mice with either control (0% TFA/total fatty acid), high TFA (16% TFA) or very high TFA (43% TFA) isocaloric diets from 2 to 16 months of age. Effects of TFA on plasma hepatic enzymes, glucose and lipid profile were minimal but very high TFA intake decreased visceral fat of non-transgenic mice. Importantly, dietary TFA increased brain TFA concentrations in a dose-related manner. Very high TFA consumption substantially modified the brain fatty acid profile by increasing mono-unsaturated fatty acids and decreasing polyunsaturated fatty acids (PUFA). Very high TFA intake induced a shift from docosahexaenoic acid (DHA, 22:6n-3) toward n-6 docosapentaenoic acid (DPA, 22:5n-6) without altering the n-3:n-6 PUFA ratio in the cortex of both control and 3xTg-AD mice. Changes in levels of Abeta(40), Abeta(42), tau protein, phosphorylated tau protein and synaptic markers were not statistically significant in the three groups of 3xTg-AD mice, despite a trend toward decreased insoluble tau in very high TFA-fed 3xTg-AD animals. In summary, TFA intake modulated brain fatty acid profiles but had no significant effect on major brain neuropathological hallmarks of AD in an animal model.

Conjugated linoleic acid alters global gene expression in human intestinal-like Caco-2 cells in an isomer-specific manner

Conjugated linoleic acid (CLA) exhibits isomer-specific effects on transepithelial calcium (Ca) transport as well as on cell growth in human intestinal-like Caco-2 cells. However, the molecular mechanisms of action are still unclear. Therefore, this study used a transcriptomic approach to help elucidate the molecular mechanisms underlying such isomer-specific effects. Caco-2 cells were treated with 80 micromol/L linoleic acid (control), 80 micromol/L trans-10, cis-12 CLA, or 80 micromol/L cis-9, trans-11 CLA for 12 d. Ca transport was measured radio-isotopically. RNA was isolated from the cells, labeled, and hybridized to the Affymetrix U133 2.0 Plus arrays (n = 3). Data and functional analysis was preformed using Bioconductor. Using a minimum fold-change criterion of 1.6 and a false discovery rate criterion of P-value <or= 0.05, trans-10, cis-12 CLA altered the expression of 918 genes, whereas, cis-9, trans-11 CLA had no effect on gene expression. Gene ontology analysis revealed that trans-10, cis-12 CLA strongly modulated a number of processes inherently related to carcinogenesis, such as cell cycle, cell proliferation, and DNA metabolism. Trans-10, cis-12 CLA, but not cis-9, trans-11 CLA, increased transepithelial Ca transport in Caco-2 cells, which corresponded to changes in molecular mediators of paracellular (including claudin 2 and 4) and transcellular (calbindin D(9)k and vitamin D receptor) Ca transport. This microarray-based study highlighted a number of gene expression patterns of relevance to 2 important intestinal processes (carcinogenesis and Ca transport), which were modulated by trans-10, cis-12 CLA. These may help our mechanistic understanding of the role of CLA in promoting gut function and health.

A Prospective Study of Trans Fatty Acids in Erythrocytes and Risk of Coronary Heart Disease

Background— High consumption of trans fat has been linked to the risk of coronary heart disease (CHD). We assessed the hypothesis that higher trans fatty acid contents in erythrocytes were associated with an elevated risk of CHD in a nested case-control study among US women.

Methods and Results— Blood samples were collected from 32 826 participants of the Nurses’ Health Study from 1989 to 1990. During 6 years of follow-up, 166 incident cases of CHD were ascertained and matched with 327 controls. Total trans fatty acid content in erythrocytes was significantly correlated with dietary intake of trans fat (correlation coefficient=0.44, P <0.01) and was associated with increased plasma low-density lipoprotein cholesterol ( P for trend =0.06), decreased plasma high-density lipoprotein cholesterol concentrations ( P for trend <0.01), and increased plasma low-density lipoprotein to high-density lipoprotein ratio ( P for trend <0.01). After adjustment for age, smoking status, and other dietary and lifestyle cardiovascular risk factors, higher total trans fatty acid content in erythrocytes was associated with an elevated risk of CHD. The multivariable relative risks (95% confidence intervals) of CHD from the lowest to highest quartiles of total trans fatty acid content in erythrocytes were 1.0 (reference), 1.6 (0.7 to 3.6), 1.6 (0.7 to 3.4), and 3.3 (1.5 to 7.2) ( P for trend <0.01). The corresponding relative risks were 1.0, 1.1, 1.3, and 3.1 ( P for trend <0.01) for a total of 18:1 trans isomers and 1.0, 1.5, 2.5, and 2.8 ( P for trend <0.01) for a total of 18:2 trans isomers.

Conclusions— These biomarker data provide further evidence that high trans fat consumption remains a significant risk factor for CHD after adjustment for covariates.

Rumenic Acid Significantly Reduces Plasma Levels of LDL and Small Dense LDL Cholesterol in Hamsters Fed a Cholesterol- and Lipid-Enriched Semi-Purified Diet

Conjugated linoleic acids (CLAs) consist of a series of positional and geometrical isomers of linoleic acid. CLA have been reported to beneficially affect cardiovascular risk factors in animal models. In order to assess the role of individual CLA isomers on lipoprotein cholesterol concentration, 30 hamsters were fed for 12 weeks an hyperlipidic diet containing pure cis-9,trans-11 CLA (c9,t11) or pure trans-10, cis-12 CLA (t10,c12) isomers given alone or as a mixture. Plasma total cholesterol, LDL and HDL cholesterol concentrations were significantly lower in the c9,t11 CLA isomer fed hamsters relative to the Control group, with the most substantially effect on LDL cholesterol (-56%; P < 0.05). Plasma triacylglycerol concentrations did not differ significantly regarding those two groups. Plasma cholesterol parameters showed a tendency to decrease in the t10,c12 CLA isomer and CLA mixture fed hamsters compared with the Control group, but differences were not significant. For the first time, the atherogenic fraction of small dense LDL was investigated. Plasma small dense LDL cholesterol concentration was lower in the c9,t11 CLA relative to Control, while the t10,c12 and CLA mixture groups showed only a non significant tendency to decrease. Taken together, these data indicate that feeding rumenic acid (c9,t11 CLA) may beneficially affect lipoprotein profile in hamster fed a cholesterol- and lipid-enriched semi-purified diet, when t10,c12 CLA isomer or CLA mixture would be less active.

Home use of margarine is an important determinant of plasma trans fatty acid status: a biomarker study

The contribution of the home use of margarines, made with partially hydrogenated vegetables oils, to total trans fatty acid intake is difficult to determine using dietary assessment because food composition databases are incomplete for trans fatty acids; moreover, hidden fats in manufactured foods may be the predominant sources of trans fatty acids. The objective of our study was to determine, using plasma phospholipid trans fatty acid composition as a surrogate measure of exposure, whether the home use of margarine or butter is an important determinant of trans fatty acid status. We conducted a community-based (Dunedin, New Zealand), cross-sectional survey of people who consumed either margarine (n 65) or butter (n 64) but not both for home use. The levels of the 18:1 trans isomers commonly found in partially hydrogenated vegetable oils were all significantly higher in the plasma phospholipids of margarine compared with butter consumers, with the exception of 18:1n-7t, which did not differ. Among margarine consumers, the percentage of total fat from margarine was significantly correlated with levels of phospholipid 18:1n-6t, 18:1n-8t and 18:1n-12/9t isomers (r 0.57-0.63, P<0.001) but only weakly with 18:1n-7t (r 0.30, P=0.016). The intake of fat from fast foods, bakery products or meat and meat products was not associated with plasma phospholipid trans isomeric composition. The home use of margarine, made with partially hydrogenated vegetable oils, is an important determinant of trans fatty acid exposure in New Zealand.

The conversion efficiency of trans-11 and trans-12 18:1 by Delta9-desaturation differs in rats

The present study evaluated and compared the efficiency of the conversion of t11 18:1 and t12 18:1 to their corresponding dienoic acids (c9,tn 18:2) and assessed whether differences due to gender existed in several tissues of rats. Three groups of 4-wk-old male and female rats were fed for 3 wk a diet supplemented with 0, 0.5, or 1% of a trans-octadecenoic acid isomer mixture (tOIM) containing t11 18:1 and t12 18:1 in equal proportion. t11 18:1 and t12 18:1 were incorporated in a tissue-specific manner, and the accrual was significant with increased dietary intake of these trans fatty acid (tFA) isomers. The t12 18:1 isomer was more readily incorporated into the rat tissues than the t11 18:1 isomer. From t11 and t12 18:1, the respective desaturase products, c9,t11 18:2 and c9,t12 18:2, were formed. The calculated conversion rates varied greatly among the tissues of the rats but they were consistently lower for t12 18:1 than for t11 18:1, suggesting that t12 18:1 is a poorer substrate than t11 18:1 for Delta9-desaturase. For both fatty acids investigated, the calculated conversion rates in decreasing order of conversion efficiency were: testes = kidneys > adipose tissue > ovaries > muscle > liver > heart. Overall, there were distinct differences in the conversion of t11 18:1 and t12 18:1, indicating that these 2 fatty acids are metabolized differently despite their structural similarities. Such metabolic differences in tFA accumulation and metabolism may have potential implication in assessing the safety of these tFA isomers because there is a positive correlation between the intake of tFA and the incidence of various diseases.

CLA isomers in milk fat from cows fed diets with high levels of unsaturated fatty acids

The concentrations of CLA isomers were determined by Ag+ -HPLC in the milk fat of cows fed a control diet consisting of hay ad libitum and 15 kg of fodder beets or this diet supplemented with oilseeds containing either high levels of oleic acid (rapeseed), linoleic acid (sunflower seed), or alphalinolenic acid (linseed). Highly significant (P < or = 0.001) correlations were found between the daily intakes of oleic acid and the concentration of the CLA isomer trans-7,cis-9 in milk fat; of linoleic acid and the CLA isomers trans-10,trans-12, trans-9,trans-11, trans-8,trans-10, trans-7,trans-9, trans-10,cis-12, cis-9,trans-11, trans-8,cis-10, and trans-7,cis-9; and of alpha-linolenic acid and the CLA isomers trans-12,trans-14, trans-11 ,trans-13, cis,trans/trans,cis-12,14, trans-11 ,cis-13, and cis-11 ,trans-13. CLA concentrations were also determined in the milk fat of cows grazing in the lowlands (600-650 m), the mountains (900-1210 m), and the highlands (1275-2120 m). The concentrations of many isomers were highest in milk fat from the highlands, but only three CLA isomers (cis-9,trans-11, trans-11 ,cis-13, and trans-8,cis-10) showed a nearly linear increase with elevation. Therefore, these three CLA isomers, and particularly the CLA isomer trans- 11,cis-13, the second-most important CLA in milk fat from cows grazing at the three altitudes, could be useful indicators of milk products of Alpine origin.

Vaccenic acid (t11-18:1) is converted to c9,t11-CLA in MCF-7 and SW480 cancer cells

The aims of this study were to determine whether vaccenic acid (VA; t11-18:1) is converted to c9,t11-CLA in human mammary (MCF-7) and colon (SW480) cancer cell lines and whether VA influences cell viability and other CLA-bioresponsive markers. When cells were incubated in the presence of VA at concentrations of 5 to 20 microg/mL, both VA and c9,t11-CLA increased in cellular lipids in a dose-dependent manner. After 4 d of incubation of SW480 and MCF-7 cells with VA (20 microg/mL), c9,t11-CLA increased from undetectable levels to 8.57 and 12.14 g/100 g FAME in cellular lipids, respectively. VA supplementation for 4 d at 5, 10, and 15 microg/mL had no effect on cell growth, whereas 20 microg/mL significantly (P < 0.05) reduced cell growth in both cell lines. VA (20 microg/mL) treatment induced DNA fragmentation and significantly (P < 0.05) depleted cytosolic GSH levels in the SW480 cell line after 4 d of incubation, suggesting that apoptosis was the mode of cell death induced by VA. Both VA and c9,t11-CLA reduced (P < 0.05) total ras expression in SW480 cells. 14C-Arachidonic acid uptake into the MG fraction was significantly increased (P < 0.05) in both cell lines while uptake into the phospholipid fraction decreased in response to VA. VA treatment significantly (P < 0.05) increased 8-epi-prostaglandin F2alpha in both cell lines. The data indicate that growth suppression and cellular responses of both cells lines are likely mediated by VA desaturation to c9,t11-CLA via delta9-desaturase.

Trans-7,cis-9 CLA is synthesized endogenously by delta9-desaturase in dairy cows

Cis-9,trans-11 and trans-7,cis-9 CLA are the most prevalent CLA isomers in milkfat. The majority of cis-9,trans-11 CLA is synthesized endogenously by delta9-desaturase. We tested the hypothesis that trans-7,cis-9 CLA originates from endogenous synthesis by inhibiting delta9-desaturase with a source of cyclopropene FA (sterculic oil: SO) or with a trans-10,cis-12 CLA supplement. Experiment 1 (four cows; Latin square) involved four treatments: control, SO, partially hydrogenated vegetable oil (PHVO), and PHVO + SO. Milk, plasma, and rumen fluid were collected. Experiment 2 treatments (four cows) were 0 or 14.0 g/d of 10,12 CLA supplement; milk and plasma were collected. Samples were analyzed by GC and Ag+-HPLC to determine FA. In Experiment 1, SO decreased milkfat content of trans-7,cis-9 CLA by 68 to 71% and cis-9,trans-11 CLA by 61 to 65%. In Experiment 2, the 10,12 CLA supplement decreased milkfat content of trans-7,cis-9 CLA and cis-9,trans-11 by 44 and 25%, respectively. Correcting for the extent of treatment-induced inhibition of delta9-desaturase based on changes in myristic and myristoleic acids, endogenous synthesis of trans-7,cis-9 CLA represented 85 and 102% in Experiments 1 and 2, respectively. Similar corrected values were 77 and 58% for endogenous synthesis of cis-9,trans-11 CLA. Thus, milkfat cis-9,trans-11 CLA was primarily from endogenous synthesis with a minor portion from rumen escape. In contrast, trans-7,cis-9 CLA was not present in rumen fluid in significant amounts. Results indicate this isomer in milkfat is derived almost exclusively from endogenous synthesis via delta9-desaturase.

Duodenal and milk trans octadecenoic acid and conjugated linoleic acid (CLA) isomers indicate that postabsorptive synthesis is the predominant source of cis-9-containing CLA in lactating dairy cows

Duodenal and milk samples obtained from lactating cows in a previous study were analyzed to compare the content and isomer distribution of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA). Four diets containing either low [25 g/100 g dry matter (DM)] or high (60 g/100 g DM) forage were fed with or without 2% added buffer to four multiparous Holstein dairy cows in a 2 x 2 factorial, 4 x 4 Latin square design with 3-wk experimental periods. Duodenal flows of CLA were low (1.02-1.84 g/d), compared with that of tFA (57-120 g/d), regardless of diet. The greatest amounts of CLA and tFA, as well as the greatest proportions of trans-10-18:1 (P < 0.02), and cis-9, trans-11 (P < 0.01) and trans-10, cis-12 CLA (P < 0.01) were in the duodenal flow of cows fed the low forage unbuffered diet. In milk fat, tFA were increased by the low forage unbuffered diet and the trans-10-18:1 (P < 0.02) replaced trans-11-18:1 as the major 18:1 isomer. Milk CLA secretion (7.2-9.1 g/d) was greater (P < 0.001) than that in the duodenal flow with each diet. This was due to the increase in cis-9, trans-11-18:2 and trans-7, cis-9 CLA, resulting most likely from endogenous synthesis via Delta9-desaturation of ruminally derived tFA. For other CLA isomers, duodenal flow was always greater than milk secretion, suggesting that they essentially were produced in the rumen.

Comparative studies on individual isomeric 18:1 acids in cow, goat, and ewe milk fats by low-temperature high-resolution capillary gas-liquid chromatography

The trans- as well as the cis-18:1 isomer profiles were established in cow, goat, and ewe cheese fats, with the assumption that these are representative of the corresponding milks. Argentation thin-layer chromatography was combined with low-temperature high-resolution gas-liquid chromatography on 100-m highly polar capillary columns, thus adding precision to earlier data for these species. Despite differences in the absolute content of trans-18:1 isomers between species, the relative profiles were essentially similar. Except for the minor trans delta6-delta8 group, all trans-18:1 isomers with their ethylenic bonds between positions delta4 and delta16 (including the resolved critical pair delta13/delta14) were separated and quantitated individually. As expected, vaccenic (trans delta9-18:1) acid was the main isomer, accounting for as much as 37 to 50% of the total fraction. It was observed that the goat trans-18:1 isomer profile was usually rather close to that of cows in winter (barn feeding), whereas that of the ewe shows a seasonal dependence. The trans-18:1 profile of ewe milk fats from this study resembles that of cows in the transition period between winter and summer (pasture) feeding. Regarding the cis-18:1 acid fraction, two isomers (oleic and cis-vaccenic acids) accounted for ca. 97% of that fraction for the three species, with the cis-delta12 isomer ranked third. The analytical procedure employed here appears a convenient alternative to oxidative-based procedures (generally ozonolysis), taking less time and alleviating some drawbacks of the latter procedure.

Conjugated linoleic acid and other anticarcinogenic agents of bovine milk fat

Prevention is an important strategy for conquering cancer. Milk fat contains a number of components, such as conjugated linoleic acid, sphingomyelin, butyric acid, ether lipids, beta-carotene, and vitamins A and D that have anticancer potential. Conjugated linoleic acid inhibits the growth of a number of human cancer cell lines and suppresses chemically-induced tumor development at a number of sites in animal models. As little as 0.1% of dietary conjugated linoleic acid inhibits the development of rat mammary tumors, independent of the amount and type of fat in the diet. Sphingomyelin, through its metabolites ceramide and sphingosine, participates in multiple antiproliferative pathways associated with suppression of carcinogenesis. Dietary sphingomyelin inhibits murine colon tumor development. Butyric acid, uniquely present in ruminant milk, is a potent antineoplastic agent and may ameliorate its potency through synergy with other milk fat components. Dietary butyric acid inhibits mammary carcinoma development in rats. In humans, ether lipids, beta-carotene, and vitamins A and D are associated with anticancer effects. Cows have the ability to extract anticarcinogenic components from pasture and feed and transfer them to milk. Use of genetic engineering and other techniques to increase the range and level of anticarcinogens in pasture and supplements may increase the anticancer potential of milk.

An optimized method for fatty acid analysis, including quantification of trans fatty acids, in human adipose tissue by gas-liquid chromatography

Considering the need for a quick direct method for measurement of the fatty acid composition including trans isomers of human adipose tissue we have developed a procedure using gas-liquid chromatography (GLC) alone, which is thus suitable for validation of fatty acid status in epidemiological studies. Fatty acids ranging in carbon number from 12 to 22 and with 0-6 double bonds were resolved and identified by capillary column GLC with a temperature program starting at 150 degrees C. Following injection, the oven temperature was increased at a rate of 3 degrees C/min to 200 degrees C, then held constant for 25 min, and finally raised at 25 degrees C/min to 225 degrees C. The trans and cis isomers of 18:1 were well separated from each other, as shown by silver-ion thin-layer chromatography. Verification by standards showed that the trans 18:1 isomers with a double bond in position 12 or lower were separated from the cis 18:1 isomers with a double bond in position 6 or higher. As the adipose tissue samples contained only small amounts of the 13t-, 14t- and 15t-18:1 isomers and the 4c- and 5c-18:1 isomers the overlapping was found to be minimal. The GLC method may also be valuable for determining the fatty acid profiles including total trans in other tissues.

Divergent incorporation of dietary trans fatty acids in different serum lipid fractions

Trans fatty acids may be involved in atherosclerotic vascular diseases. We investigated the incorporation of dietary trans fatty acids and oleic acid into the serum triglycerides (TG), cholesterol esters (CE), and phospholipids (PL). Fourteen healthy female volunteers, aged 23.2+/-3.1 yr (mean+/-SD), body mass index 20.8+/-2.1 kg/m2 participated in this study. All subjects consumed both a trans fatty acid-enriched diet (TRANS diet) and an oleic acid-enriched diet (OLEIC diet) for 4 wk according to a randomized crossover design. Both experimental diet periods were preceded by consumption of a baseline diet for 2 wk which supplied 37% of total energy (E%) as fat: 18 E% from saturated fatty acids (SFA), 12 E% from monounsaturated fatty acids, and 6 E% from polyunsaturated fatty acids. Five E% of the SFA in the baseline diet was replaced by trans fatty acids (18:1t and 18:2c,t + 18:2t,t, where c is cis and t is trans) in the TRANS diet and by oleic acid (18:1n-9) in the OLEIC diet. After the TRANS diet, the proportions of 18:1t and 18:2t increased (P<0.001) in all serum lipid fractions analyzed. The increase of 18:1t in TG and PL (1.80+/-0.28 vs. 5.26+/-1.40; 1.07+/-0.34 vs. 3.39+/-0.76 mol% of total fatty acids, respectively) was markedly higher than that in CE (0.44+/-0.07 vs. 0.92+/-0.26), whereas that of 18:2t was nearly the same in all three fractions. The proportions of palmitic, stearic, arachidonic, and eicosapentaenoic acids in TG, CE, and PL and that of oleic acid in TG and CE were decreased when compared with the baseline value. In contrast, the proportion of palmitoleic acid in TG and PL and that of linoleic acid in PL increased on the TRANS diet. After consumption of the OLEIC diet, the proportion of oleic acid increased in all three lipid fractions analyzed, and the percentage increase was nearly the same in all fractions. In contrast, the proportions of 18:1t in TG and PL and 18:2t in TG and CE decreased when compared with the baseline value. In conclusion, a moderate increase in dietary trans fatty acids resulted in a marked incorporation into serum lipids and decreased the conversion of linoleic acid to its more unsaturated long-chain metabolites. Analysis of 18:1t from serum TG and PL seems to reflect reliably the dietary intake of this fatty acid.

Unusual fatty acids in the depot fat of the Canadian beaver (Castor canadensis)

Unusual fatty acids in the adipose tissue of the Canadian beaver were analysed by argentation thin-layer chromatography, gas-liquid chromatography and gas chromatography-mass spectrometry of several adducts and spectroscopic measurements. The total proportion of trans-octadecenoic fatty acids and the distribution of double bonds in these acids resembled those of ruminant fats. Because trans-11-18:1 was the main trans-18:1 isomer of beaver fat and a conjugated diene cis-9, trans-11-18:2 was also detected, it can be deduced that linoleic acid (cis-9, cis-12-18:2) is biohydrogenated in the beaver. The ideas that microbial processes intervene before normal absorption and fatty acid metabolism of the beaver is also supported by the larger amounts of anteiso odd-chain fatty acids with respect to the corresponding iso acids in the beaver depots. In addition, the distribution of double bonds in the cis-octadecenoic acids was wide, as it is in the depot fats of ruminants.

Trans fatty acids: a cause for concern?

The recommendation to reduce total and saturated fat is incorporated into the dietary guidelines for the general population in many western countries. In addition, dietary modification to reduce substantially the intake of saturated fats is a cornerstone of treatment in the hyperlipidaemias. Concern has recently been expressed regarding possible deleterious effects of trans isomers of unsaturated fatty acids on the lipoprotein profiles of both normo and hypercholesterolaemic persons. This review seeks to examine recent research in this area with a view to considering possible changes in the present dietary recommendations.

Trans fatty acids: implications for health, analytical methods, incidence in edible fats and intake (a review)

Trans fatty acids (TFA) are supposed to be related to a variety of physiological effects. Numerous studies in this field are gathered and compared, which mainly deal with the influences on lipoprotein levels in plasma and their effects with regard to coronary heart diseases. Furthermore, the analytical accessibility of trans fatty acids by different methods is presented. Thus, the most reliable method for an exact quantitation of trans fatty acids in edible fats is the combination of Ag-TLC with GC. The contents of TFA, in particular trans-octadecenoic acids, in bovine and human milk fat, in partially hydrogenated vegetable fats and oils as well as in processed food from different countries, determined in numerous studies, are summarized. Especially results on the isomeric distribution of positional isomers of trans-octadecenoic acid may be of future interest, since negative metabolic activities might only originate from certain isomers. Finally, intake rates of TFA in several countries are presented. It can be concluded that there still is need for further nutritional studies and that the discussion about TFA should not neglect the comparison with the saturated fatty acids C12, C14 and C16.

[Content of trans-fatty acids in food]

The fatty acid composition of the fat in 197 food samples has been analyzed by gas liquid chromatography. The use of a 30 m capillary column coated with CPSil88 permitted the separation of the cis and trans isomers. The trans fatty acid content of milk and milk products ranged from 1.9 to 7.9%. Meat samples from ruminants contained 2.0-10.6% trans fatty acids. In pork fat the amounts were less than 0.5%. Sausages and other meat products contained high levels of pork fat. Therefore these samples contained less than 1% trans fatty acids, with the exception of some pure beef products. The amounts of trans fatty acids in foods which may contain hydrogenated oils ranged from 0 to 34.9%. In food samples with high levels of trans fatty acids lower contents of saturated fatty acids were analyzed.

Trans-fatty acids intake and risk of myocardial infarction

BACKGROUND

Concern that trans-fatty acids formed in the partial hydrogenation of vegetable oils may increase the risk of coronary disease has existed for several decades, but direct evidence on this relation in humans is limited.

METHODS AND RESULTS

With a case-control design, we studied the association between intake of trans-fatty acids and a first acute myocardial infarction among 239 patients admitted to one of six hospitals in the Boston area and 282 population control subjects. Intake of trans-fatty acids was estimated using a previously validated food frequency questionnaire. After adjustment for age, sex, and energy intake, intake of trans-fatty acids was directly related to risk of myocardial infarction (relative risk for highest compared with lowest quintile, 2.44; 95% confidence interval, 1.42, 4.19; for trend P < .0001). This relation remained highly significant after adjustment for established coronary risk factors, multivitamin use, and intake of saturated fat, monounsaturated fat, linoleic acid, dietary cholesterol, vitamins E and C, carotene, and fiber. Intake of margarine--the major source of trans-isomers--was significantly associated with risk of myocardial infarction.

CONCLUSIONS

These data support the hypothesis that intake of partially hydrogenated vegetable oils may contribute to the risk of myocardial infarction.

Trans monounsaturated fatty acids in nutrition and their impact on serum lipoprotein levels in man

Trans-C18:1 in the diet originate predominantly from partially hydrogenated oils, with beef, mutton and dairy products being an additional source. These fatty acids are absorbed and incorporated into lipids. Their estimated consumption is about 5-7% of total fatty acids, although reliable data are lacking. In addition, large variations between individuals exist. There is no evidence that trans fatty acids accumulate in human tissues. Elaidic acid and its positional isomers do, however, raise LDL cholesterol and apoprotein B and Lp(a) and probably depress HDL cholesterol and apoprotein A-I, compared with the cis isomer, oleic acid. In view of these adverse effects, patients at high risk for atherosclerosis, in addition to reducing their intake of saturated fatty acids and of cholesterol might also do well to avoid excessive intakes of trans fatty acids. Still, trans fatty acids form only a minor component of the diets of most patients and therefore even marked relative reductions in intake will probably have less of an impact on LDL cholesterol than a sizeable reduction in saturated fatty acids and cholesterol will produce.

[Intake of trans-isomeric fatty acids--an evaluation on the basis of data of the national consumption study in 1991]

The intake of trans octadecenoic acids is estimated by a national consumption assay. The daily intake in West Germany differs between 3.4 g for women and 4.1 g for men. The consumption of trans fatty acids decreased in the last years, due to the progress in food technology and changes in nutritional habits. The main sources of trans fatty acids are partially hydrogenated vegetable fats just as well as ruminant and dairy fats.