Caspase pathway of elaidic acid (9t-C18:1)-induced apoptosis in human umbilical vein endothelial cells

Although TFAs (trans fatty acids) do have effects on many endothelial functions, systemic inflammation and immune disorders, only limited experimental evidence is available that TFAs participate in the pathogenesis of endothelial cell apoptosis. HUVEC (human umbilical vein endothelial cells) were grown in medium with elaidic acid (9t-C18:1) at 50, 100, 200 and 400 μmol/l for 24 h. Apoptosis was measured by flow cytometry, and caspase 3, 8 and 9 activities by colorimetric assay and their mRNA expression by qRT-PCR (quantitative real-time PCR). Results showed that 9t-C18:1 induced apoptosis of HUVEC in a dose-dependent manner. The activities and mRNA expression of caspases 8, 9 and 3 were significantly increased compared with that of the control. Z-IETD-FMK and Z-LEHD-FMK inhibited the activation of caspase 3 and apoptosis induced by 9t-C18:1. Also Z-IETD-FMK inhibited the activation of caspase 9. mRNA expressions of Bid and Smac (second mitochondria-derived activator of caspase)/DIABLO [direct IAP (inhibitor of apoptosis)-binding protein with low pI] were also significantly elevated. We conclude that 9t-C18:1 induces apoptosis of HUVEC through activating caspases 8, 9 and 3. The death receptor pathway and the mitochondrial pathway both participated in the apoptosis course induced by 9t-C18:1.     

Comparison of cis and trans fatty acid containing phosphatidylcholines on membrane properties

The ever-increasing amount of trans fatty acids in the human diet has been linked to a variety of afflictions, most notably coronary heart disease and arteriosclerosis. The mechanism of why the replacement of cis fatty acids with their trans counterparts can be detrimental to the health of an individual remains a mystery. Here, we compare the differences in membrane physical properties including molecular dynamics, lateral lipid packing, thermotropic phase behavior, "fluidity", lateral mobility, and permeability between model membranes (lipid monolayers and bilayers) composed of cis- and trans-containing phosphatidylcholines (PCs). The PCs tested have a total of zero, one, two, or four cis (oleic or linoleic) or trans (elaidic or linoelaidic) double bonds. These experiments all confirm the basic hypothesis that trans fatty acids produce membrane properties more similar to those of saturated chains than to those of acyl chains containing cis double bonds; i.e., cis double bonds induce much larger membrane perturbations than trans double bonds.     

LR-90 prevents methylglyoxal-induced oxidative stress and apoptosis in human endothelial cells

Methylglyoxal (MGO) is a highly reactive dicarbonyl compound known to induce cellular injury and cytoxicity, including apoptosis in vascular cells. Vascular endothelial cell apoptosis has been implicated in the pathophysiology and progression of atherosclerosis. We investigated whether the advanced glycation end-product inhibitor LR-90 could prevent MGO-induced apoptosis in human umbilical vascular endothelial cells (HUVECs). HUVECs were pre-treated with LR-90 and then stimulated with MGO. Cell morphology, cytotoxicity and apoptosis were evaluated by light microscopy, MTT assay, and Annexin V-FITC and propidium iodide double staining, respectively. Levels of Bax, Bcl-2, cytochrome c, mitogen-activated protein kinases (MAPKs) and caspase activities were assessed by Western blotting. Reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. LR-90 dose-dependently prevented MGO-associated HUVEC cytotoxicity and apoptotic biochemical changes such as loss of MMP, increased Bax/Bcl-2 protein ratio, mitochondrial cytochrome c release and activation of caspase-3 and 9. Additionally, LR-90 blocked intracellular ROS formation and MAPK (p44/p42, p38, JNK) activation, though the latter seem to be not directly involved in MGO-induced HUVEC apoptosis. LR-90 prevents MGO-induced HUVEC apoptosis by inhibiting ROS and associated mitochondrial-dependent apoptotic signaling cascades, suggesting that LR-90 possess cytoprotective ability which could be beneficial in prevention of diabetic related-atherosclerosis.     

Trans Fatty Acids Enhanced Beta-Amyloid Induced Oxidative Stress in Nerve Growth Factor Differentiated PC12 Cells

The effects of trans fatty acids, elaidic acid (trans-9, C18:1) and linoelaidic acid (trans-9, trans-12 C18:2), at 20 or 40 μM in nerve growth factor differentiated PC12 cells with or without beta-amyloid peptide (Aβ) were examined. Elaidic acid treatment alone did not affect cell viability and oxidative injury associated markers (P > 0.05). However, co-treatments of elaidic acid and Aβ led to more reduction in mitochondrial membrane potential (MMP) and Na⁺-K⁺-ATPase activity, and more increase in DNA fragmentation and 8-hydroxydeoxyguanosine (8-OHdG) production than Aβ treatment alone (P < 0.05). Linoelaidic acid alone exhibited apoptotic and oxidative effects in cells via decreasing MMP and Na⁺-K⁺-ATPase activity, increasing reactive oxygen species (ROS) level, lowering glutathione content and glutathione peroxidase (GPX) activity (P < 0.05). The co-treatments of linoelaidic acid with Aβ further enhanced oxidative damage via enhancing the generation of ROS, nitrite oxide and 8-OHdG, elevating caspase-3, caspase-8 and nitric oxide synthase activities, as well as declining GPX, catalase and superoxide dismutase activities (P < 0.05). These results suggested that the interaction of linoelaidic acid and Aβ promoted oxidative stress and impaired mitochondrial functions in neuronal cells.     

4-Hydroxynonenal induces dysfunction and apoptosis of cultured endothelial cells.

Lipolytic products of triglyceride-rich lipoproteins, i.e., free fatty acids, may cause activation and dysfunction of the vascular endothelium. Mechanisms of these effects may include lipid peroxidation. One of the major and biologically active products of peroxidation of n-6 fatty acids, such as linoleic acid or arachidonic acid, is the aldehyde 4-hydroxynonenal (HNE). To study the hypothesis that HNE may be a critical factor in endothelial cell dysfunction caused by free fatty acids, human umbilical endothelial cells (HUVEC) were treated with up to160 microM of linoleic or arachidonic acid. HNE formation was detected by immunocytochemistry in cells treated for 24 h with either fatty acid, but more markedly with arachidonic acid. To study the cellulareffects of HNE, HUVEC were treated with different concentrations of this aldehyde, and several markers of endothelial cell dysfunction were determined. Exposure to HNE for 6 and 9 h resulted in increased cellular oxidative stress. However, short time treatment with HNE did not cause activation of nuclear factor-kappaB (NF-kappaB). In addition, HUVEC exposure to HNE caused a dose-dependent decrease in production of both interleukin-8 (IL-8) and intercellular adhesion molecule-1 (ICAM-1). On the other hand, HNE exerted prominent cytotoxic effects in cultured HUVEC, manifested by morphological changes, diminished cellular viability, and impaired endothelial barrier function. Furthermore, HNE treatment induced apoptosis of HUVEC. These data provide evidence that HNE does not contribute to NF-kappaB-related mechanisms of the inflammatory response in HUVEC, but rather to endothelial dysfunction, cytotoxicity, and apoptotic cell death.     

Saturated free fatty acids,palmitic acid and stearic acid,induce apoptosis by stimulation of ceramide generation in rat testicular Leydig cell

In men, obesity has generally been associated with reduced plasma testosterone levels and with elevation of the plasma free fatty acids (FFAs). In this study, we investigated the effects of saturated FFAs including palmitic acid (PA) and stearic acid (SA), and polyunsaturated FFA arachidonic acid (AA) on the survival of rat testicular Leydig cell cultured in vitro. PA and SA markedly suppressed Leydig cell survival in a time- and dose-dependent manner. In contrast, AA stimulated the cell proliferation at 5-10 times of physiological concentration. The suppressive effect of PA and SA on cell survival was caused by apoptosis evidenced by DNA ladder formation and Annexin V-EGFP/propidium iodide staining of the cells. The apoptotic effect of PA was possibly mediated by ceramide generation because it could be completely blocked by ceramide synthase inhibitor fumonisin B1 and exogenous ceramide itself could directly induce apoptosis in vitro. Surprisingly, the apoptosis induced by PA could be partly prevented by AA. These results indicate that PA and SA induce apoptosis in testicular Leydig cells by ceramide production and these apoptotic effects may be a possible mechanism for reproductive abnormalities in obese men, and AA can partly prevent the apoptotic effect induced by saturated FFA.     

Long-term effects of cis and trans monounsaturated (18:1) and saturated (16:0) fatty acids on the synthesis and secretion of apolipoprotein A-I- and apolipoprotein B-containing lipoproteins in HepG2 cells

The objective of this study was to compare the long-term effects of oleic (cis 18:1), elaidic (trans 18:1), and palmitic (16:0) acids on hepatic lipoprotein production, using HepG2 cells as an experimental model. The net accumulation in the medium of apolipoprotein A-I (apoA-I) was not significantly altered by fatty acids, whereas that of apoB was increased with oleic and elaidic acids. Oleic acid, and to a lesser extent elaidic and palmitic acids, increased the mass of triglycerides in the medium and the incorporation of [(3)H]glycerol into secreted triglycerides. The incorporation of [(14)C]acetate into cellular and secreted total cholesterol was stimulated by 96% and 83%, respectively, with elaidic acid but was not significantly modified by oleic or palmitic acid. Relative to oleic acid, the secretion of (14)C-labeled phospholipids and triglycerides was decreased 28% to 31% with elaidic and palmitic acids whereas that of free cholesterol and cholesteryl esters was enhanced 93% and 73%, respectively, with elaidic acid but remained unchanged with palmitic acid. Compared with oleic acid, elaidic acid stimulated the secretion of very low density lipoprotein cholesterol (VLDL-Chol), low density lipoprotein cholesterol (LDL-Chol), and high density lipoprotein cholesterol (HDL-Chol) by 43%, 70%, and 34%, respectively, whereas palmitic acid decreased VLDL-Chol but had no significant effect on LDL-Chol and HDL-Chol. The ratios of total cholesterol to HDL-Chol were 3.17, 3.60, and 3.25 with oleic, elaidic, and palmitic acids, respectively; the corresponding ratios of LDL-Chol to HDL-Chol were 0.87, 1.10, and 0.93, respectively. Compared with oleic and palmitic acids, the LDL and HDL particles secreted in the presence of elaidic acid contained higher levels of free cholesterol and cholesteryl esters and a lower content of phospholipids. The phospholipid-to-total cholesterol ratios of HDL were 1.05, 0.40, and 0.76 with oleic, elaidic, and palmitic acids, respectively.Our results indicate that in comparison with cis monounsaturated and saturated fatty acids, trans fatty acids have more adverse effects on the concentration and composition of lipoproteins secreted by HepG2 cells.     

Effects of ethanol on pancreatic beta-cell death: interaction with glucose and fatty acids

Western lifestyle plays an important role in the prevalence of type 2 diabetes by causing insulin resistance and pancreatic β-cell dysfunction, a prerequisite for the development of diabetes. High fat diet and alcohol are major components of the western diet. The aim of the present study was to investigate the effects of ethanol and fatty acids on β-cell survival and metabolism. We treated the rat β-cell line RINm5F with ethanol, a mixture of palmitic and oleic acids, or both. Reactive oxygen species (ROS) were determined by (5-(and-6)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate) (CM-H2DCFDA) fluorescence assay, and mitochondrial activity was assessed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) reduction assay and by determining ATP production. Cell viability was assessed with a cell counter and trypan blue exclusion, and the mode of cell death by Hoechst33342 and propidium iodide staining. With both ethanol and fatty acid treatments, MTT reduction and ATP production decreased, whereas ROS production increased. Ethanol treatment had no effect on cell number, whereas fatty acid treatment reduced the cell number. Cell incubation with ethanol, fatty acids, or both increased the number of Hoechst 33342-positive nuclei. However, the majority of nuclei from fatty acid-treated cells were stained with propidium iodide, indicating a loss of plasma membrane integrity. We conclude that both ethanol and fatty acids generate cellular oxidative stress, and affect mitochondrial function in RINm5F β-cells. However, ethanol causes β-cell death by apoptosis, whereas fatty acids cause cell death predominantly by necrosis. It is not known whether these results are applicable to human β-cells.     

The Roles of ROS and Caspases in TRAIL-Induced Apoptosis and Necroptosis in Human Pancreatic Cancer Cells

Death signaling provided by tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) can induce death in cancer cells with little cytotoxicity to normal cells; this cell death has been thought to involve caspase-dependent apoptosis. Reactive oxygen species (ROS) are also mediators that induce cell death, but their roles in TRAIL-induced apoptosis have not been elucidated fully. In the current study, we investigated ROS and caspases in human pancreatic cancer cells undergoing two different types of TRAIL-induced cell death, apoptosis and necroptosis. TRAIL treatment increased ROS in two TRAIL-sensitive pancreatic cancer cell lines, MiaPaCa-2 and BxPC-3, but ROS were involved in TRAIL-induced apoptosis only in MiaPaCa-2 cells. Unexpectedly, inhibition of ROS by either N-acetyl-L-cysteine (NAC), a peroxide inhibitor, or Tempol, a superoxide inhibitor, increased the annexin V-/propidium iodide (PI)⁺ early necrotic population in TRAIL-treated cells. Additionally, both necrostatin-1, an inhibitor of receptor-interacting protein kinase 1 (RIP1), and siRNA-mediated knockdown of RIP3 decreased the annexin V^-/PI⁺ early necrotic population after TRAIL treatment. Furthermore, an increase in early apoptosis was induced in TRAIL-treated cancer cells under inhibition of either caspase-2 or -9. Caspase-2 worked upstream of caspase-9, and no crosstalk was observed between ROS and caspase-2/-9 in TRAIL-treated cells. Together, these results indicate that ROS contribute to TRAIL-induced apoptosis in MiaPaCa-2 cells, and that ROS play an inhibitory role in TRAIL-induced necroptosis of MiaPaCa-2 and BxPC-3 cells, with caspase-2 and -9 playing regulatory roles in this process.     

Comparison of the effect of individual saturated and unsaturated fatty acids on cell growth and death induction in the human pancreatic beta-cell line NES2Y

We tested the effects of various types of fatty acids, differing in the degree of saturation and in the cis/trans configuration of the double bond, on the growth and viability of NES2Y cells (a human pancreatic beta-cell line). We found that during a 48-hour incubation period, saturated fatty acids, i.e. palmitic and stearic acids, at a physiologically relevant concentration of 1 mM and higher concentrations induced death of the beta-cells while their counterpart unsaturated fatty acids, i.e. palmitoleic and oleic acids, did not induce cell death at concentrations up to 3 mM. We also found that unsaturated elaidic acid with a trans double bond exerted significant inhibition of growth of the beta-cells at a concentration approximately ten times lower, i.e. 0.1 mM vs. 1 mM, than counterpart oleic acid with a cis double bond. This is the first direct evidence that a trans unsaturated fatty acid is significantly more effective in inhibiting beta-cell growth than a counterpart cis unsaturated fatty acid. Furthermore, we newly demonstrated that beta-cell death induced by saturated fatty acids is related to significant increase of caspase-2 activity (2 to 5-fold increase) but not to caspase-3 activation. The growth-inhibiting effect of saturated fatty acids at concentrations lower than death-inducing concentrations correlates with certain increase of caspase-2 activity.     

Trans fatty acids induce vascular inflammation and reduce vascular nitric oxide production in endothelial cells

Intake of trans fatty acids (TFA), which are consumed by eating foods made from partially hydrogenated vegetable oils, is associated with a higher risk of cardiovascular disease. This relation can be explained by many factors including TFA's negative effect on endothelial function and reduced nitric oxide (NO) bioavailability. In this study we investigated the effects of three different TFA (2 common isomers of C18 found in partially hydrogenated vegetable oil and a C18 isomer found from ruminant-derived-dairy products and meat) on endothelial NF-κB activation and nitric oxide (NO) production. Human endothelial cells were treated with increasing concentrations of Elaidic (trans-C18:1 (9 trans)), Linoelaidic (trans-C18:2 (9 trans, 12 trans)), and Transvaccenic (trans-C18:1 (11 trans)) for 3 h. Both Elaidic and Linoelaidic acids were associated with increasing NF-κB activation as measured by IL-6 levels and phosphorylation of IκBα, and impairment of endothelial insulin signaling and NO production, whereas Transvaccenic acid was not associated with these responses. We also measured superoxide production, which has been hypothesized to be necessary in fatty acid-dependent activation of NF-κB. Both Elaidic acid and Linoelaidic acid are associated with increased superoxide production, whereas Transvaccenic acid (which did not induce inflammatory responses) did not increase superoxide production. We observed differential activation of endothelial superoxide production, NF-κB activation, and reduction in NO production by different C18 isomers suggesting that the location and number of trans double bonds effect endothelial NF-κB activation.     

Short-term and long-term effects of fatty acids in rat hepatoma AS-30D cells: the way to apoptosis

Arachidonic acid and, to a smaller extent, oleic acid at micromolar concentrations decreased the mitochondrial membrane potential within AS-30D rat hepatoma cells cultivated in vitro and increased cell respiration. The uncoupling effect of both fatty acids on cell respiration was partly prevented by cyclosporin A, blocker of the mitochondrial permeability transition pore. Arachidonic acid increased the rate of reactive oxygen species (ROS) production, while oleic acid decreased it. Both fatty acids induced apoptotic cell death of AS-30D cells, accompanied by the release of cytochrome c from mitochondria to the cytosol, activation of caspase-3 and association of proapoptotic Bax protein with mitochondria; arachidonic acid being a more potent inducer than oleic acid. Trolox, a potent antioxidant, prevented ROS increase induced by arachidonic acid and protected the cells against apoptosis produced by this fatty acid. It is concluded that arachidonic and oleic acids induce apoptosis of AS-30D hepatoma cells by the mitochondrial pathway but differ in the mechanism of their action: Arachidonic acid induces apoptosis mainly by stimulating ROS production, whereas oleic acid may contribute to programmed cell death by activation of the mitochondrial permeability transition pore.     

Effects of insulin-like growth factor-1 on okadaic acid-induced apoptosis in SH-SY5Y cells

The effects of insulin-like growth factor-1 (IGF-1) on the cytotoxicity and apoptosis induced by okadaic acid (OA) in SH-SY5Y cells were investigated. Cell viability was measured using the MTT (3-(4,5-dimethylthiazolyl-2)-2,-5-diphenyltetrazolium bromide) assay. Early and late apoptosis/necrosis were analyzed by flow cytometry using Annexin V and propidium iodide (PI) double-staining. Caspase-3 activation was detected by Western blot analysis. Preincubation with IGF-1 for 24 h prevented cytotoxicity induced by 40 nM OA given for 24 h, and the MTT value significantly increased. Incubation with 20 nM OA for 24 h caused a marked increase in the percentage of early apoptotic and late apoptotic/necrotic cells, which was not dependent on the activation of caspase-3. OA-induced apoptosis was significantly decreased by pretreatment with 10 ng/ml of IGF-1 for 24 h. The results supported the hypothesis that IGF-1 may be useful in the treatment of Alzheimer's disease.     

Reactive oxidizing species produced near the plasma membrane induce apoptosis in bovine aorta endothelial cells

Many cytotoxic agents initiate apoptosis by generating reactive oxidizing species (ROS). The goal of this study was to determine whether apoptosis could be induced by initial reactions of ROS near the plasma membrane. Bovine aorta endothelial cells (BAEC) were illuminated with evanescent wave visible radiation, which has limited penetration into the basal surface of cells, or by trans-radiation. Imaging of fluorescent dyes localizing in the plasma membrane, mitochondria, or nucleus confirmed that evanescent wave radiation excited only dyes in and near the plasma membrane. Singlet oxygen, an ROS generated by photosensitization, has a very short lifetime, ensuring that it oxidizes molecules residing in or very close to the plasma membrane when evanescent wave radiation is used. Cells with condensed nuclei were considered apoptotic and were quantified after treatment with varying doses of light. Annexin V staining without propidium iodide staining confirmed that these cells were apoptotic. The doses required to induce apoptosis using evanescent wave radiation were 10-fold greater than those needed for trans-irradiation. Quantitative analysis of the evanescent wave penetration into cells supports a mechanism in which the singlet oxygen created near the plasma membrane, rather than at intracellular sites, was responsible for initiation of apoptosis.     

Differential effects of cis and trans fatty acid isomers, oleic and elaidic acids, on the cholesteryl ester transfer protein activity.

In a previous publication (Lagrost, L. and Barter, P.J. (1991) Biochim. Biophys. Acta 1085, 209-216), saturated and cis unsaturated non-esterified fatty acids have been shown to modulate the rate at which cholesteryl esters are transferred from high-density lipoproteins (HDL) to low-density lipoproteins (LDL) in the presence of the human cholesteryl ester transfer protein (CETP). In the present report, the effects of cis (oleic acid) and trans (elaidic acid) monounsaturated isomers on the CETP-mediated transfer of cholesteryl esters between HDL and LDL were compared. Mixtures of human LDL and HDL3, containing or not radiolabelled cholesteryl esters, were incubated at 37 degrees C with CETP in the presence or in the absence of either stearic (18:0), oleic (18:1 cis) or elaidic (18:1 trans) acids. It was observed that oleic acid and elaidic acid had different effects on the CETP-mediated redistribution of radiolabelled cholesteryl esters as well as on the net mass transfer of cholesterol from HDL3 to LDL. In particular, at high non-esterified fatty acid/lipoprotein ratio, the transfer of cholesteryl esters was significantly inhibited by the cis isomer and increased by the trans isomer.     

Metformin prevents methylglyoxal-induced apoptosis by suppressing oxidative stress in vitro and in vivo

Methylglyoxal (MGO) is an active metabolite of glucose and plays a prominent role in the pathogenesis of diabetic vascular complications, including endothelial cell apoptosis induced by oxidative stress. Metformin (MET), a widely prescribed antidiabetic agent, appears to reduce excessive reactive oxygen species (ROS) generation and limit cell apoptosis. However, the molecular mechanisms underlying this process are still not fully elucidated. We reported here that MET prevents MGO-induced apoptosis by suppressing oxidative stress in vitro and in vivo. Protein expression and protein phosphorylation were investigated using western blotting, ELISA, and immunohistochemical staining, respectively. Cell viability and apoptosis were assessed by the MTT assay, TUNEL staining, and Annexin V-FITC and propidium iodide double staining. ROS generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. Our results revealed that MET prevented MGO-induced HUVEC apoptosis, inhibited apoptosis-associated biochemical changes such as loss of MMP, the elevation of the Bax/Bcl-2 ratio, and activation of cleaved caspase-3, and attenuated MGO-induced mitochondrial morphological alterations in a dose-dependent manner. MET pretreatment also significantly suppressed MGO-stimulated ROS production, increased signaling through the ROS-mediated PI3K/Akt and Nrf2/HO-1 pathways, and markedly elevated the levels of its downstream antioxidants. Finally, similar results were obtained in vivo, and we demonstrated that MET prevented MGO-induced oxidative damage, apoptosis, and inflammation. As expected, MET reversed MGO-induced downregulation of Nrf2 and p-Akt. In addition, a PI3K inhibitor (LY-294002) and a Nrf2 inhibitor (ML385) observably attenuated the protective effects of MET on MGO-induced apoptosis and ROS generation by inhibiting the Nrf2/HO-1 pathways, while a ROS scavenger (NAC) and a permeability transition pores inhibitor (CsA) completely reversed these effects. Collectively, these findings broaden our understanding of the mechanism by which MET regulates apoptosis induced by MGO under oxidative stress conditions, with important implications regarding the potential application of MET for the treatment of diabetic vascular complications.Subject terms: Apoptosis, Stress signalling     

Saturated Fatty Acid Requirer of Neurospora crassa

Dietary saturated fatty acids containing 12- to 18-carbon atoms satisfy growth requirements of Neurospora crassa mutant cel (previously named ol; Perkins et al., reference 11); unsaturated fatty acids are synthesized by direct desaturation when an appropriate saturate is available. Odd-chain saturates, 15 carbons and 17 carbons long, satisfy the requirement, and elaidic acid (18:1 Delta(9)trans) results in slow growth. Oleic acid and other cis-unsaturated fatty acids do not satisfy growth requirements; however, oleic acid plus elaidic acid result in growth at a faster rate than elaidate alone. The use of a spin-label fatty acid reveals that hyphae produced by cel during a slow basal level of growth have lipids that reflect a relatively rigid state of viscosity compared to wild type. cel Supplemented with fatty acids and wild type supplemented in the same way have lipids of the same viscosities as reflected by electron spin resonance.     

Isomerization of stable isotopically labeled elaidic acid to cis and trans monoenes by ruminal microbes

A previous study showed that oleic acid was converted by mixed ruminal microbes to stearic acid and also converted to a multitude of trans octadecenoic acid isomers. This study traced the metabolism of one of these trans C18:1 isomers upon its incubation with mixed ruminal microbes. Unlabeled and labeled (18-[13C]trans-9 C18:1) elaidic acid were each added to four in vitro batch cultures with three cultures inoculated with mixed ruminal bacteria and one uninoculated culture. Samples were taken at 0, 12, 24, and 48 h and analyzed for 13C enrichment in component fatty acids by gas chromatography-mass spectrometry. At 0 h of incubation, enrichment was detected only in elaidic acid. By 48 h of incubation, 13C enrichment was 18% (P < 0.01) for stearic acid, 7% to 30% (P < 0.01) for all trans C18:1 isomers having double bonds between carbons six through 16, and 5% to 10% for cis-9 and cis-11 monoenes. After 48 h, 13C enrichment in the uninoculated cultures was only detected in the added elaidic acid. This study shows trans fatty acids exposed to active ruminal cultures are converted to stearic acid but also undergo enzymic isomerization yielding a multitude of positional and geometric isomers.