Linoleic Acid Metabolite DiHOME Decreases Post-ischemic Cardiac Recovery in Murine Hearts

Cardiac ischemia/reperfusion injury is associated with the formation and action of lipid mediators derived from polyunsaturated fatty acids. Among them, linoleic acid (LA) is metabolized to epoxyoctadecanoic acids (EpOMEs) by cytochrome P450 (CYP) epoxygenases and further to dihydroxyoctadecanoic acids (DiHOMEs) by soluble epoxide hydrolase (sEH). We hypothesized that EpOMEs and/or DiHOMEs may affect cardiac post-ischemic recovery and addressed this question using isolated murine hearts in a Langendorff system. Hearts from C57Bl6 mice were exposed to 12,13-EpOME, 12,13-DiHOME, or vehicle (phosphate buffered sodium; PBS). Effects on basal cardiac function and functional recovery during reperfusion following 20 min of ischemia were investigated. Electrocardiogram (ECG), left ventricular (LV) pressure and coronary flow (CF) were continuously measured. Ischemia reperfusion experiments were repeated after administration of the sEH-inhibitor 12-(3-adamantan-1-yl-ureido)dodecanoic acid (AUDA). At a concentration of 100 nM, both EpOME and DiHOME decreased post-ischemic functional recovery in murine hearts. There was no effect on basal cardiac parameters. The detrimental effects seen with EpOME, but not DiHOME, were averted by sEH inhibition (AUDA). Our results indicate that LA-derived mediators EpOME/DiHOME may play an important role in cardiac ischemic events. Inhibition of sEH could provide a novel treatment option to prevent detrimental DiHOME effects in acute cardiac ischemia.

Inhibition of Candida albicans and Staphylococcus aureus biofilms by centipede oil and linoleic acid

Microbial biofilms are associated with persistent infections because of their high tolerance to antimicrobial agents and host defenses. The effects of centipede oil from Scolopendra subspinipes mutilans and its main components were investigated to identify non-toxic biofilm inhibitors. Centipede oil and linoleic acid at 20 µg ml^-1 markedly inhibited biofilm formation by two fluconazole-resistant Candida albicans strains and three Staphylococcus aureus strains without affecting their planktonic cell growth. Also, both centipede oil and linoleic acid inhibited hyphal growth and cell aggregation by C. albicans. In addition, centipede oil and linoleic acid showed anti-biofilm activities against mixed C. albicans and S. aureus biofilms. Transcriptomic analysis showed that centipede oil and linoleic acid downregulated the expressions of several hypha/biofilm-related genes in C. albicans and α-hemolysin in S. aureus. Furthermore, both compounds effectively reduced C. albicans virulence in a nematode infection model with minimal toxicity.

Inhibitory Effects of Scutellaria baicalensis Root Extract on Linoleic Acid Hydroperoxide-induced Lung Mitochondrial Lipid Peroxidation and Antioxidant Activities

In this study, we evaluated the ability of Scutellaria baicalensis Georgi to protect lipid-peroxidation (LPO) in lung tissue after free radical-induced injury. We prepared S. baicalensis root (SBR) extracts using different solvents. The total flavonoid and total phenol contents of each extract were measured, and the ROS damage protection was evaluated by analyzing linoleic acid hydroperoxide (LHP)-induced LPO in rat lung mitochondria. Moreover, evaluating diphenylpicrylhydrazyl (DPPH), hydrogen peroxide, superoxide anion radical, and hydroxyl radical scavenging abilities and using metal chelating assays were used to determine in vitro antioxidant activity. The ethyl acetate (EtOAc) extract showed high ROS scavenging ability, and four compounds were subsequently isolated and purified from this extract: baicalin, baicalein, wogonin, and oroxylin A. Baicalein in rat lung mitochondria the most significant LHP-induced LPO inhibition was shown and extracted with EtOAc that contained the highest amount of baicalein. Thus, baicalein and the EtOAc extract of SBR may be efficient in conferring ROS damage protection and inhibiting LHP-induced LPO in rat lung mitochondria. Additional studies are warranted to investigate their use as antioxidant therapy for respiration infections, nutrition supplements, and lead compounds in pharmaceuticals.

Responses of unicellular alga Chlorella pyrenoidosa to allelochemical linoleic acid

Linoleic acid (LA), is the product of secondary metabolism secreted from Microcystis aeruginosa, and it exhibits allelopathic activity against eukaryotic algae. However, information about on the mechanisms associated with the inhibition of algal activity by LA is limited. In this study, Chlorella pyrenoidosa was treated with LA (20-120 μg L^-1) for 4 days, and its growth inhibition and physiological responses were examined for potential toxic mechanisms. The photosynthetic efficiency of C. pyrenoidosa was inhibited by LA treatments, and the F_v/F_m parameter decreased significantly compared to that of controls; however, the photosynthetic pigment content did not change significantly. Peroxidase activity was enhanced, relieving oxidative damage in algae after LA treatments. However, superoxide dismutase and catalase were suppressed, ultimately leading to the aggravation of lipid peroxidation. Transcriptome-based gene expression analysis revealed that the 120 μg L^-1 LA treatment significantly inhibited the transcription of genes related to photosynthesis, carbon metabolism, and amino acid metabolism in C. pyrenoidosa, suggesting that these genes might be key LA targets in C. pyrenoidosa. Moreover, the expression of genes involved in vitamin, lipid, nitrogen cycling, terpenoid, and ascorbate metabolism was also affected, suggesting that LA inhibits algal cell growth through multiple pathways. The identification of LA-responsive genes in C. pyrenoidosa provides new insight into LA stress responses in eukaryotic algae.

Resilience of small intestinal beneficial bacteria to the toxicity of soybean oil fatty acids

Over the past century, soybean oil (SBO) consumption in the United States increased dramatically. The main SBO fatty acid, linoleic acid (18:2), inhibits in vitro the growth of lactobacilli, beneficial members of the small intestinal microbiota. Human-associated lactobacilli have declined in prevalence in Western microbiomes, but how dietary changes may have impacted their ecology is unclear. Here, we compared the in vitro and in vivo effects of 18:2 on Lactobacillus reuteri and L. johnsonii. Directed evolution in vitro in both species led to strong 18:2 resistance with mutations in genes for lipid biosynthesis, acid stress, and the cell membrane or wall. Small-intestinal Lactobacillus populations in mice were unaffected by chronic and acute 18:2 exposure, yet harbored both 18:2- sensitive and resistant strains. This work shows that extant small intestinal lactobacilli are protected from toxic dietary components via the gut environment as well as their own capacity to evolve resistance.

Dehydroepiandrosterone prevents linoleic acid-induced endothelial cell senescence by increasing autophagy

BACKGROUND

Autophagy has emerged as a potentially important factor in the pathogenesis of atherosclerosis. Dehydroepiandrosterone (DHEA) is an adrenal steroid of great recent interest due to its anti-aging and anti-atherogenic effects; however, little is known about its role in autophagy and endothelial senescence.

OBJECTIVE

The aim of this study was to investigate whether DHEA prevents linoleic acid (LA)-induced endothelial senescence by enhancing autophagy.

MATERIALS/METHODS

After pre-treatement with or without DHEA prior to LA treatment in human aortic endothelial cells (HAECs), the level of senescence was compared by senescence-associated acidic β-galactosidase (SA-β-Gal) staining and hyperphosphorylated pRB (ppRB) protein level. Autophagy was detected by LC3 conversion and measuring the level of p62/SQSTM1 (sequestosome 1), a protein degraded by autophagy. The fusion of autophagosome and lysosome was confirmed by fluorescence microscopy.

RESULTS

Pre-treatment with DHEA inhibited LA-induced endothelial senescence. DHEA increased the conversion of LC3-I to LC3-II and decreased the level of p62 in a time- and dose-dependent manner. Although both DHEA and LA treatment increased the conversion of LC3-I to LC3-II, treatment of LA increased p62 and decreased fusion of autophagosome and lysosome, which reflected decreased autophagic flux. However, pre-treatment with DHEA restored autophagic flux inhibited by LA. When we evaluated signaling pathways, we found that JNK activation involved in LC3 conversion induced by DHEA.

CONCLUSION

DHEA prevents LA-induced endothelial senescence by restoring autophagy and autophagic flux through JNK activation.

Linoleic acid induces red blood cells and hemoglobin damage via oxidative mechanism

Hidden blood loss typically occurs following total hip arthroplasty (THA) and total knee arthroplasty (TKA) and is thought to be related to free fatty acid (FFA). To study the effect of linoleic acid on red blood cells and to examine the pathogenesis of hidden blood loss in vivo, we generated an animal model by injecting linoleic acid into the tail veins of rats. We collected blood samples and determined red blood cell count (RBC) and levels of hemoglobin (Hb), as well as the oxidation and reducing agents in the blood, including glutathione peroxidase (GSH-PX), total superoxide dismutase (T-SOD), hydrogen peroxide (H2O2), and ferryl hemoglobin (Fe4+=O2-), which is generated by the oxidation of Hb. Hidden blood loss occurred when linoleic acid was administered at a concentration of 60 mmol/L; RBC and Hb levels were significantly reduced by 24 h post-injection. This was followed by erythrocyte deformation, reduced activity of GSH-PX and T-SOD, and decreased levels of H2O2. This was accompanied by an increase in ferryl species, which likely contributes to oxidative stress in vivo. Our findings suggest that linoleic acid enhances acute red blood cell injury. Hb and RBC began to increase by 72 h, potentially resulting from linoleic acid metabolism. Thus, elevated levels of linoleic acid in the blood cause acute oxidative damage to red blood cells, eventually leading to partial acute anemia. These findings highlight the pathophysiology underlying hidden blood loss.

Effects of bolus injection of soybean-based fat emulsion and fatty acids on pulmonary gas exchange function

To determine whether or not a "bolus injection" of soybean-based fat emulsion (SFE), which contains oleic acid (OA), a potent lung-toxic unsaturated C-18 fatty acid, can induce pulmonary dysfunction, we examined the effect of SFE injection on the partial oxygen pressure of arterial blood (Pao2) and pulmonary vascular permeability. In addition, we compared the effect of an injection of SFE with that of OA, soybean oil (a source of SFE), emulsified OA and C-18 fatty acids. Bolus injection of SFE (0.3-4.8 ml/kg) had little effect on Pao2) and pulmonary vascular permeability. Injection of an equivalent amount of OA, on the other hand, significantly decreased Pao2 and increased pulmonary vascular hyper-permeability. This decrease in Pao2 was attenuated by emulsification. Unemulsified soybean oil also induced a decrease in Pao2, although the effect was weaker than that of OA. Other unsaturated C-18 fatty acids (linoleic and linolenic acid) induced a decrease in Pao2 as potent as OA while stearic acid, a C-18 saturated fatty acid, had little effect. Although we did not observe pulmonary toxicity as a result of "bolus injection" of SFE, the chemical form, for example, emulsification and the degree of saturability of the carbon chain, seems to influence the pulmonary toxicities of lipids and fatty acids. Furthermore, the potent pulmonary toxicity of OA seems to depend not only on pulmonary vascular embolization but also pharmacological and/or inflammation-inducing properties.

Phytotoxic compounds from roots of Centaurea diffusa Lam

An extract of roots of Centaurea diffusa (diffuse knapweed) yielded caryophyllene oxide and linoleic acid which were shown to be phytotoxic. Also isolated were germacrene B, a previously-known phytotoxin as well as the inactive polyene aplotaxene. A combination of these compounds, if transferred to the soil, could be one factor in the invasive behavior of this weed. Contrary to a literature report, 8-hydroxyquinoline was not detected in root exudates of in vitro grown C. diffusa nor could it be identified in the root extract. However, a recent report from a different group maintains that 8-hydroxyquinoline can be released from roots of C. diffusa following a diurnal rhythm.

Etheno-DNA adduct formation in rats gavaged with linoleic acid, oleic acid and coconut oil is organ- and gender specific

Intake of linoleic acid (LA) increased etheno-DNA adducts induced by lipid peroxidation (LPO) in white blood cells (WBC) of female but not of male volunteers [J. Nair, C.E. Vaca, I. Velic, M. Mutanen, L.M. Valsta, H. Bartsch, High dietary omega-6 polyunsaturated fatty acids drastically increase the formation of etheno-DNA adducts in white blood cells of female subjects, Cancer Epidemiol. Biomarkers Prev. 6 (1997) 597-601]. Etheno-adducts were measured in rats gavaged with LA, oleic acid (OA) and saturated fatty acid rich coconut oil for 30 days. DNA from organs and total WBC was analyzed for 1, N(6)-ethenodeoxyadenosine (varepsilondA) and 3, N(4)-ethenodeoxycytidine (varepsilondC) by immunoaffinity/(32)P-postlabeling. Colon was the most affected target with LA-treatment, where etheno-adducts were significantly elevated in both sexes. In WBC both adducts were elevated only in LA-treated females. Unexpectedly, OA treatment enhanced etheno-adduct levels in prostate 3-9 fold. Our results in rodents confirm the gender-specific increase of etheno-adducts in WBC-DNA, likely due to LPO induced by redox-cycling of 4-hydroxyestradiol. Colon was a target for LPO-derived DNA-adducts in both LA-treated male and female rats, supporting their role in omega-6 PUFA induced colon carcinogenesis.

Metabolism of polyunsaturated fatty acids and their toxicity to the microflora of the rumen

Ruminal microorganisms hydrogenate polyunsaturated fatty acids (PUFA) present in forages and thereby restrict the availability of health-promoting PUFA in meat and milk. The aim of this study was to investigate PUFA metabolism and the influence of PUFA on members of the ruminal microflora. Eleven of 26 predominant species of ruminal bacteria metabolised linoleic acid (LA; cis-9,cis-12-18:2) substantially. The most common product was vaccenic acid (trans-11-18:1), produced by species related to Butyrivibrio fibrisolvens. alpha-Linolenic acid (LNA; cis-9,cis-12,cis-15-18:3) was metabolised mostly by the same species. The fish oil fatty acids, eicosapentaenoic acid (EPA; 20:5(n - 3)) and docosahexaenoic acid (DHA; 22:6(n - 3)) were not metabolised. Cellulolytic bacteria did not grow in the presence of any PUFA at 50 microg ml(-1), nor did some butyrate-producing bacteria, including the stearate producer Clostridium proteoclasticum, Butyrivibrio hungatei and Eubacterium ruminantium. Toxicity to growth was ranked EPA > DHA > LNA > LA. Cell integrity, as measured using propidium iodide, was damaged by LA in all 26 bacteria, but to different extents. Correlations between its effects on growth and apparent effects on cell integrity in different bacteria were low. Combined effects of LA and sodium lactate in E. ruminantium and C. proteoclasticum indicated that LA toxicity is linked to metabolism in butyrate-producing bacteria. PUFA also inhibited the growth of the cellulolytic ruminal fungi, with Neocallimastix frontalis producing small amounts of cis-9,trans-11-18:2 (CLA) from LA. Thus, while dietary PUFA might be useful in suppressing the numbers of biohydrogenating ruminal bacteria, particularly C. proteoclasticum, care should be taken to avoid unwanted effects in suppressing cellulolysis.

Characterization of the potent neuroprotective properties of the natural vitamin E alpha-tocotrienol

The natural vitamin E tocotrienols possess properties not shared by tocopherols. Nanomolar alpha-tocotrienol, not alpha-tocopherol, is potently neuroprotective. On a concentration basis, this finding represents the most potent of all biological functions exhibited by any natural vitamin E molecule. We sought to dissect the antioxidant-independent and -dependent neuroprotective properties of alpha-tocotrienol by using two different triggers of neurotoxicity, homocysteic acid (HCA) and linoleic acid. Both HCA and linoleic acid caused neurotoxicity with comparable features, such as increased ratio of oxidized to reduced glutathione GSSG/GSH, raised intracellular calcium concentration and compromised mitochondrial membrane potential. Mechanisms underlying HCA-induced neurodegeneration were comparable to those in the path implicated in glutamate-induced neurotoxicity. Inducible activation of c-Src and 12-lipoxygenase (12-Lox) represented early events in that pathway. Overexpression of active c-Src or 12-Lox sensitized cells to HCA-induced death. Nanomolar alpha-tocotrienol was protective. Knock-down of c-Src or 12-Lox attenuated HCA-induced neurotoxicity. Oxidative stress represented a late event in HCA-induced death. The observation that micromolar, but not nanomolar, alpha-tocotrienol functions as an antioxidant was verified in a model involving linoleic acid-induced oxidative stress and cell death. Oral supplementation of alpha-tocotrienol to humans results in a peak plasma concentration of 3 microm. Thus, oral alpha-tocotrienol may be neuroprotective by antioxidant-independent as well as antioxidant-dependent mechanisms.

Increased expression of a molecular chaperone GroEL in response to unsaturated fatty acids by the biohydrogenating ruminal bacterium,Butyrivibrio fibrisolvens

Butyrivibrio fibrisolvens is the most active bacterial species in the biohydrogenation of polyunsaturated fatty acids (PUFA) in the rumen. It needs to remove the unsaturated bonds in order to detoxify the PUFA to enable the growth of the bacterium. Here, we investigated the response of cell membrane-associated proteins in B. fibrisolvens to growth in the presence of PUFA. Numerous changes were observed in the cell membrane-associated proteome. One of the main modifications occurring when the 18:2 fatty acids, linoleic acid and conjugated linoleic acid, were added, was an increased expression of the molecular chaperone GroEL.

Mechanisms involved in Jurkat cell death induced by oleic and linoleic acids

BACKGROUND & AIMS

Previous study from our laboratory showed the toxicity of oleic (OA) and linoleic acids (LA) on Jurkat and Raji cells and human lymphocytes in vitro. The mechanisms involved in the toxicity induced by OA and LA on Jurkat cells were determined in vitro.

METHODS

Jurkat cells were treated in the presence of OA and LA (25, 50, 100 and 200muM). The parameters investigated were: triglycerides and cholesterol ester concentrations determined by enzymatic assay, activation of peroxisome proliferator activated receptor (PPAR) by electrophoretic mobility shift assay, caspase 3, 6 and 8 activities by spectrofluorometric assay, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma production by enzyme linked absorbent assay (ELISA), expression of pro- (Bax) and anti- (Bcl-2) apoptotic genes by real time polymerase chain reaction and expression of pleiotropic genes by macroarray technique

RESULTS

Evidence is presented herein that the increase in triglycerides concentrations induced by OA is more pronounced than that caused by LA in Jurkat cells. Importantly, triglycerides accumulation may be a mechanism to protect lymphocytes against the toxicity induced by fatty acids. Both fatty acids raised PPAR activation, caspase 3 and 6 activities and TNF-alpha production. LA in toxic concentrations modulated the expression of genes related to cell cycle, apoptosis, proliferation, oxidative stress, and cytokine receptors.

CONCLUSION

The findings reported herein support the cell death induced by OA and LA involved triglycerides accumulation, PPAR activation, caspase 3 and 6 activities and TNF-alpha production.

Fatty acid-induced toxicity and neutral lipid accumulation in insulin-producing RINm5F cells

Fatty acids have been shown to cause death of rat and human primary pancreatic beta cells and of insulin-producing cell lines. These studies focused mainly on saturated and monounsaturated FA such as palmitic, stearic and oleic acids. In this study, we have performed a comparison of the toxicity of a wider range of FA. The toxicity of different FA to insulin-producing RINm5F cells was assessed by flow cytometry measuring loss of plasma membrane integrity and increase in DNA fragmentation. Additionally, the FA induced neutral lipid accumulation and the FA composition were determined. Palmitic, linoleic, gamma-linolenic, oleic, stearic, and eicosapentaenoic acid caused DNA fragmentation of insulin-producing RINm5F cells. Loss of membrane integrity was mainly caused by linoleic and gamma-linolenic acid. There was no correlation between cytotoxicity and the abundance of the FA in the cells as determined by HPLC analysis. Taken as whole, the toxic effect of the FA on insulin-producing RINm5F cells varied irrespective of the chain length and the degree of unsaturation. In these cells PA and LA exhibited the highest toxicity, whereas AA was not toxic. In addition, the toxicity of most tested FA was inversely related to low NLA, except for AA and EPA. The results of this study contribute to the understanding of the role of FA in the impairment of pancreatic beta cell function that occurs in type 2 diabetes and obesity.

Application of a continuous bioreactor cascade to study the effect of linoleic acid on hybridoma cell physiology

The aim of the present study is to demonstrate the use of controlled bioreactors for toxicological studies. As a model system the effect of linoleic acid on hybridoma cells is studied in two well-controlled continuously operated bioreactors placed in series. In the first reactor the effect on rapid proliferating cells can be studied, while in the second reactor a special steady state is created, which allows studying the effect on apoptotic cells. Experiments are done at 0, 25, and 50 microM linoleic acid. At the end of the experiment with 50 microM linoleic acid, the concentration of linoleic acid is increased stepwise to determine the cytotoxic level. For rapid proliferating cells exposed to 25 and 50 microM stimulation of growth was observed. At 50 microM there was at the same time an increase in cell death through apoptosis. For stressed apoptotic cells linoleic acid caused partial growth inhibition at 25 and 50 microM and arrest of cell proliferation in the G(2)/M phase at 50 microM. For both, rapid proliferating cells and stressed apoptotic cells, complete growth inhibition occurred at 85 microM, with cells being arrested in the G(2)/M phase and dying mainly through necrosis. Cells in the bioreactor system appeared to be more sensitive towards linoleic acid than cells grown in multi-well plates. (IC(50) = 300 microM; IC(100) = 400 microM). Altogether the results of the present study reveal that the biostat experiments allow detailed analysis of the effect of a bioactive ingredient on cell physiology and behavior.

Comparative toxicity of oleic and linoleic acid on human lymphocytes

Commercially available lipid emulsions for parenteral nutrition are mainly composed by long chain triacylglycerol containing a high proportion of linoleic acid (LA) or oleic acid (OA). The immunological impact of such therapy is particularly important because parenteral diets are often administered to critically ill patients as a mechanism to supply adequate nutrition during catabolic stress conditions. The comparative toxicity of OA and LA on human lymphocytes and the type of cell death induced by these fatty acids were determined in vitro. Parameters of cell death were investigated by flow cytometry-cell viability, DNA fragmentation, phosphatidylserine externalization, mitochondrial depolarization, neutral lipid accumulation and production of reactive oxygen species-and by fluorescence microscopy-chromatin condensation. Additionally a spectrofluorometric assay was employed to determine the activities of caspase--3, 6 and 8. Evidence is presented herein that OA is less toxic to human lymphocytes than LA. However, both fatty acids promoted apoptosis and necrosis of these cells. The mechanism of cell death induced by OA involved activation of caspase 3 while the mechanism of death induced by LA involved mitochondrial depolarization and ROS production. Importantly, neutral lipid accumulation may be a mechanism to protect lymphocytes against the toxicity induced by OA. OA may offer an immunological less problematic alternative to LA with respect to fatty acid composition of parenteral nutritional emulsions.

Comparative toxicity of oleic acid and linoleic acid on Raji cells

OBJECTIVE

Parenteral diets are often administered to critically ill patients. To study one of the effects of commercially available parenteral lipid diets, rich in triacylglycerol esters of omega-6 polyunsaturated fatty acids or omega-9 monounsaturated fatty acids, on the immune system of such patients, we evaluated the cytotoxicity of oleic and linoleic acids on Raji cells that had been derived from human B-lymphocytes.

METHODS

Cell death intensity and type were investigated by flow cytometry by quantitation of cell volume, granularity, DNA fragmentation, mitochondrial depolarization, and lipid accumulation. Fluorescence microscopy was used to determine chromatin condensation and type of cell death (acridine orange/ethidium bromide assay). Gene expression of BCL-XL, BCL-XS, C-MYC, and P53 was studied by reverse transcriptase polymerase chain reaction.

RESULTS

Oleic acid was less toxic than linoleic acid to Raji cells. Both fatty acids promote apoptosis and necrosis of these cells. The mechanism of cell death induced by these fatty acids seemed to involve mitochondrial depolarization, lipid accumulation, and overexpression of C-MYC and P53.

CONCLUSION

Oleic acid may offer a less harmful alternative to linoleic acid in parenteral diets with respect to patient B-lymphocyte-mediated immunologic activity.

Comparative toxicity of oleic acid and linoleic acid on Jurkat cells

BACKGROUND

Lipid emulsions for parenteral nutrition commercially available are mainly composed of long-chain triacylglycerol containing a high proportion of alpha-6 polyunsaturated fatty acids or alpha-9 monounsaturated fatty acids. The immunological impact of such therapy is particularly important because parenteral and enteral diets are often administered to critical ill patients. The comparative toxicity of oleic acid and linoleic acid on Jurkat cells, a human T lymphocyte cell line, and the type of cell death induced by these fatty acids were determined.

METHODS

Cell death was investigated by cytometry: decrease in cell volume, increase of granularity, DNA fragmentation, phosphatidylserine externalization, mitochondrial depolarization, lipid accumulation; by fluorescence microscopy: chromatin condensation and acridine orange/ethidium bromide assay; and by RT-PCR: mRNA expression of apoptotic genes.

RESULTS

Evidence is presented herein that oleic acid is much less toxic to Jurkat cells than linoleic acid. Both fatty acids promote apoptosis and necrosis of these cells. The mechanism of cell death induced by these fatty acids seem to involve with mitochondrial depolarization, lipid accumulation and the levels of C-MYC and P53 mRNA expression.

CONCLUSION

Therefore, oleic acid may offer an immunological less harmful alternative to linoleic acid for parenteral and enteral diets preparation.

A subchronic 90-day oral rat toxicity study and in vitro genotoxicity studies with a conjugated linoleic acid product

Conjugated linoleic acid (CLA) is the term given to a group of positional and geometric isomers of the essential fatty acid linoleic acid. CLA is found naturally in foods such as dairy and meat products. CLA is reported to have a number of beneficial effects including anticarcinogenic activity. However, safety data are limited. Clarinol G80 is a commercial preparation containing equal amounts of the 9cis,11trans and 10trans,12cis CLA isomers in the form of glycerides. In order to support the safety-in-use of Clarinol G80 as an ingredient in food, the preparation was tested in two in vitro mutagenicity assays, an Ames test and an in vitro cytogenetics assay, and a 90-day repeat-dose oral toxicity rat study. Clarinol G80 was non-mutagenic in both in vitro assays. In the 90-day study, Clarinol G80 produced hepatocellular hypertrophy in female rats at the highest dose level (15% w/w). This effect was an adaptive effect in response to feeding high levels of Clarinol G80 in the diet and was reversible upon withdrawal of test material. An increase in plasma insulin levels was also observed female rats fed 15% w/w Clarinol G80 but there was no effect on plasma glucose levels. A No Observed Adverse Effect Level of 2433 mg/kg bw/day for male and 2728 mg/kg bw/day female rats was identified in the study.

Perfluorooctyl bromide (perflubron) attenuates oxidative injury to biological and nonbiological systems

OBJECTIVE

To examine whether perfluorooctyl bromide (perflubron) is capable of protecting biological and nonbiological systems against oxidative damage through a mechanism independent of its known anti-inflammatory property.

DESIGN

A controlled, in vitro laboratory study.

SETTING

Research laboratory of a health sciences university.

SUBJECTS

Rat pulmonary artery endothelial cell cultures (biological system) and linoleic acid in sodium dodecyl sulfate micelles (nonbiological system).

INTERVENTIONS

Rat pulmonary artery endothelial cells labeled with dichlorofluorescein diacetate and incubated with perflubron or culture media (control) were exposed to H2O2. H2O2-induced fluorescence of dichlorofluorescein diacetate was measured as an index of intracellular oxidative stress. In another experiment, linoleic acid in sodium dodecyl sulfate micelles was exposed to various concentrations of the azo initiator 2,2'-diazo-bis-(2-amidinopropane) dihydrochloride (2, 4, 20, and 50 mM) in the presence or absence of perflubron. Malondialdehyde measurements were obtained as a marker of oxidative damage to linoleic acid.

MEASUREMENTS AND MAIN RESULTS

Cell monolayers incubated with perflubron exhibited 66.6% attenuation in intracellular fluorescence compared with controls (p < .05). Linoleic acid in sodium dodecyl sulfate micelles incubated with perflubron and exposed to 2, 4, 20, or 50 mM of 2,2'-diazo-bis-(2-amidinopropane) dihydrochloride showed less evidence of lipid peroxidation as indicated by lower malondialdehyde measurements at 240 mins (10.6%, 16%, 41%, and 14.2%, respectively) compared with controls.

CONCLUSIONS

Perflubron attenuates oxidative damage to both biological and nonbiological systems. This newly recognized property of perflubron is independent of its anti-inflammatory properties.

Analysis of oxidative DNA damage after human dietary supplementation with linoleic acid

It has been hypothesized that oxygen radicals generated by peroxidation of dietary linoleic acid may induce genetic damage and thereby increase cancer risk. We examined the effect of dietary supplementation with linoleic acid on the levels of oxidative DNA damage in peripheral lymphocytes and on the blood plasma antioxidant potential. Thirty volunteers received during 6 weeks either a high dose of linoleic acid (15 g/day), an intermediate dose of linoleic acid (7.5 g/day) or an isocaloric supplement without linoleic acid (15 g palmitic acid/day). After the intervention, no significant increase in oxidative DNA damage, measured as relative amounts of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) in DNA from peripheral lymphocytes, was observed in both high and intermediate linoleic acid-supplemented groups (increase of respectively 13 and 21%; P>0.05). Also, the differences between levels of oxidative DNA damage in the high or intermediate linoleic acid-supplemented group and the control group receiving palmitic acid (23% decrease) were not significant. Furthermore, no statistically significant differences were found between the total antioxidant capacities of blood plasma from the different experimental groups. Plasma levels of malondialdehyde, an important end-product of lipid peroxidation, were not increased after supplementation, nor were effects found on the plasma concentrations of retinol, alpha-tocopherol and beta-carotene. Despite the experimental design that excludes several forms of bias introduced in studies based on modulation of dietary composition, our results provide no indication of increased oxidative stress or genetic damage as a result of increased dietary intake of linoleic acid. Therefore, we see no scientific basis to reconsider the public health policy to stimulate the intake of polyunsaturated fatty acids aimed at the reduction of coronary heart diseases.

Final report on the amended safety assessment of diisopropyl dimer dilinoleate, dicetearyl dimer dilinoleate, diisostearyl dimer dilinoleate, dioctyl dimer dilinoleate, dioctyldodecyl dimer dilinoleate, and ditridecyl dimer dilinoleate

Diisopropyl Dimer Dilinoleate, Dicetearyl Dimer Dilinoleate, Diisostearyl Dimer Dilinoleate, Dioctyl Dimer Dilinoleate, Dioctyldodecyl Dimer Dilinoleate, and Ditridecyl Dimer Dilinoleate are diesters of their respective alcohols and dilinoleic acid. They function as skin-conditioning agents in a variety of cosmetic products at concentrations around 10%, but may be used at concentrations up to 53% in lipsticks. These ingredients do not absorb radiation in the ultraviolet (UV) UVA or UVB range and the only impurities expected are <0.5% dilinoleic acid, <0.1% isopropyl alcohol or <1% isostearyl alcohol, and/or small amounts of dilinoleic acid and cetearyl alcohol or octyldodecanol, depending on which diester is used. The potential skin penetration of these ingredients was evaluated using an estimate of the octanol/water partition coefficient (logP of 17.7) based on the structure of Diisopropyl Dimer Dilinoleate. This is consistent with the insolubility of these ingredients in water. Safety test data on dilinoleic acid (no adverse effects) were considered relevant because dilinoleic acid is a component of these diesters and a likely breakdown product. The acute oral and dermal LD(50) values for rats of Diisopropyl, Diisostearyl, and Dioctyldodecyl Dimer Dilinoleate were >5.0 g/kg. In a subchronic feeding study, macrophage aggregation was seen in the mesenteric lymph node at the lowest dose level (0.1% in the diet). These ingredients did not produce skin or ocular irritation in animal tests, nor were they comedogenic. Ames testing, clastogenesis in human lymphocytes in culture, and L5178Y mouse lymphoma cell forward mutations were all negative, indicating no dilinoleic acid genotoxicity. No carcinogenicity or reproductive/developmental toxicity data were available; however, structural alerts that would suggest a mutagenic or carcinogenic risk are absent. Significant reproductive/developmental toxicity or other systemic toxicity is not expected with these ingredients because they remain on the skin surface. In clinical studies, cosmetic formulations containing these ingredients did not produce skin irritation or sensitization, although one report of sensitization to dilinoleic acid appeared in the case literature. The Panel did note that the concentration of use of Diisopropyl Dimer Dilinoleate was reportedly as high as 53% in lipsticks, but that the highest concentration tested for irritation/sensitization is 27%. Given the size of these molecules, their relative insolubility in water, their lipophilic nature, and the absence of any significant case reports of allergic reactions, a use concentration of 53% is not likely to be associated with any adverse effects. Accordingly, these diesters were considered safe as used in cosmetic products.

Effect of linoleic acid metabolites on Na(+)/K(+) pump current in N20.1 oligodendrocytes: role of membrane fluidity

Metabolic derivatives of linoleic acid, both monoepoxides and diols, have been reported to be toxic in humans and multiple animal tissue preparations. A previous electrophysiological study has shown these compounds produce multiple effects on the electrical activity of rat ventricular myocytes. The hydrophobic nature of these compounds suggests the possibility that these effects may be due to nonspecific lipid interactions, i.e., changes in membrane fluidity. This study investigates membrane fluidity as a possible mechanism by which linoleic acid metabolites inhibit Na(+)/K(+) pump current (I(p)). This study showed that positional isomers 9,10- and 12,13-epoxy-octadecenoic acid (EOA) and 9,10- and 12,13-dihydroxy-OA (DHOA) inhibit I(p) in a dose-dependent manner in N20.1 mouse oligodendrocytes, with greater inhibition produced by EOAs. These compounds, at 10 microM, inhibited I(p) by 4.7 +/- 1.6, 18.2 +/- 0.5, 11.7 +/- 0.5, and 25.1 +/- 0.9% for 12,13-DHOA, 9,10-DHOA, 12,13-EOA, and 9,10-EOA, respectively, in oligodendrocytes. Fluorescence recovery after photobleaching measurements showed that both DHOA isomers produced a 7-8% increase in diffusion coefficient of the probe at 10 microM, whereas the diffusion coefficient was decreased by 5 and 13% by 9,10-EOA and 12,13-EOA, respectively. There was no apparent correlation between membrane fluidity and inhibition of I(p) by these four linoleic acid metabolites. These results indicate that membrane fluidity alone cannot explain the effects of these compounds on I(p) and suggest that they have a specific interaction with the Na(+)/K(+) pump.

Troglitazone ameliorates lipotoxicity in the beta cell line INS-1 expressing PPAR gamma

To elucidate the mechanisms by which troglitazone, which is a direct ligand for peroxisome proliferator-activated receptor (PPAR) gamma, ameliorates insulin resistance, we have demonstrated that PPAR gamma is expressed in a pancreatic beta cell line, INS-1, using reverse transcription-polymerase chain reaction (RT-PCR). We incubated the cells with 5 micromol/l troglitazone and 1 mmol/l of each major free fatty acid (FFA; palmitic acid, oleic acid, and linoleic acid), alone or in combination, for 48 h. After that, we evaluated glucose-stimulated insulin secretion (GSIS) and 25 mmol/l KCl-induced insulin secretion in the presence of diazoxide, which clamps membrane potential. Our results showed: (1) treatment with troglitazone for 48 h caused enhancement of GSIS, although troglitazone significantly suppressed cell viability assessed by MTT assay. (2) In cells co-treated with troglitazone and FFA, troglitazone ameliorated lipotoxicity due to FFA. (3) In the presence of 300 micromol/l diazoxide and 25 mmol/l KCl, troglitazone did not affect the recovery of GSIS in INS-1 cells. These results suggest that insulin secretion from the rat insulinoma cell line, INS-1, is modulated by troglitazone, acting somewhere in the ATP-sensitive K(+) channel pathway, possibly through PPAR gamma.

Linoleic acid, cis-epoxyoctadecenoic acids, and dihydroxyoctadecadienoic acids are toxic to Sf-21 cells in the absence of albumin

Conversion of 12,13-cis-epoxyoctadecenoic acid (12,13-EOA) to 12,13-dihydroxyoctadecenoic acid (12,13-DHOA) by soluble epoxide hydrolase has been suggested to be a critical step in mediating the toxicity of epoxidized linoleic acid. The current study tests the hypothesis that low levels of albumin in the normal culturing media of Sf-21 cells can protect these cells from exposures to 12,13-EOA, but not 12,13-DHOA. In albumin-free media, Sf-21 cells exposed to 100 microM 12,13-EOA, and 12,13-DHOA for 1 min showed significant signs of mitochondrial dysfunction which led to cytotoxicity. The addition of bovine serum albumin (BSA) at a concentration (3 microM) found in normal serum-supplemented media protected Sf-21 cells exposed to 12,13-EOA, but not 12,13-DHOA while BSA (500 microM) fully protected Sf-21 cells exposed to these fatty acids. These data resolve previous discrepancies observed among in vitro models and help clarify our understanding of how these metabolites affect human health.

Analysis of the toxic effects of linoleic acid, 12,13-cis-epoxyoctadecenoic acid, and 12,13-dihydroxyoctadecenoic acid in rabbit renal cortical mitochondria

P450 epoxidation of linoleic acid has been associated with many pathological conditions that often lead to acute renal failure. However, there is only suggestive evidence that linoleic acid monoepoxides and/or linoleic diols directly induce mitochondrial dysfunction. Using isolated rabbit renal cortical mitochondria (RCM), we found that linoleic acid (50 microM) and the linoleic acid monoepoxide, cis-12,13-epoxy-9-octadecenoic acid (12,13-EOA, 50 microM) increased state 4 and oligomycin-insensitive respiration and reduced state 3 and oligomycin-sensitive respiration. Concomitant with these effects, linoleic acid and 12,13-EOA decreased mitochondrial membrane potential (DeltaPsi). In contrast, the hydrolyzed product of 12,13-EOA, 12,13-dihydroxyoctadecenoic acid (12,13-DHOA, 50 microM), had no effect on state 3, state 4, oligomycin-sensitive, and oligomycin-insensitive respiration, and DeltaPsi. Neither linoleic acid or its metabolites altered uncoupled respiration, which suggests that these compounds have no affect on electron transport chain in RCM. Nucleotides such as ATP (0.5 mM) and GDP (0.5 mM) partially prevented the decrease in DeltaPsi but did not attenuate the increase in oligomycin-insensitive respiration after exposure to linoleic acid (50 microM) and 12,13-EOA (50 microM). These results demonstrate that linoleic acid metabolism to the 12,13-DHOA is a detoxification pathway that prevents mitochondrial dysfunction in RCM. The increase in state 4 respiration concomitant with decreases in state 3 respiration and DeltaPsi suggest that, in addition to uncoupling effects, linoleic acid and 12,13-EOA may have other effects, such as alterations of mitochondrial membranes. The inability of ATP and GDP to fully attenuate the uncoupling effects of linoleic acid and 12,13-EOA suggests that these effects are mediated through a nucleotide-independent mechanism.

Defining mechanisms of toxicity for linoleic acid monoepoxides and diols in Sf-21 cells

Linoleic acid monoepoxides have been correlated with many pathological conditions. Studies using insect cells derived from Spodoptera frugiperda (Sf-21 cells) have suggested that conversion of the epoxides to the diols is required for toxicity. However, more recent studies using rabbit renal proximal tubules have suggested that linoleic acid monoepoxides are direct mitochondrial toxins. To better understand these discrepancies, we compared the toxicity of these linoleic acid metabolites in Sf-21 cells using mitochondrial respiration as an end point. Linoleic acid (100 microM) and 12,13-epoxy-9-octadecenoic acid (12,13-EOA, 100 microM) increased the rate of oligomycin-insensitive respiration by approximately 3.5- and 3-fold, respectively, decreased the rate of oligomycin-sensitive respiration by approximately 52 and 68%, respectively, and had no effect on the integrity of the electron transport chain. These effects were concentration-dependent, occurred within 1 min, and recovered to basal levels within 45 min. 12,13-Dihydroxy-9-octadecenoic acid (12,13-DHOA, 100 microM) had no effect on oligomycin-insensitive respiration but decreased the rate of oligomycin-sensitive respiration and uncoupled respiration in a concentration-dependent manner. Approximately 79 and 68% of oligomycin-sensitive respiration and uncoupled respiration was inhibited by 12,13-DHOA (100 microM), respectively. These effects occurred within 1 min and were not reversible in 6 h. Effects similar to those induced by 12,13-DHOA (100 microM) were observed using 12,13-EOA (100 microM) in Sf-21 cells expressing human soluble epoxide hydrolase. These data suggest that in this Sf-21 model linoleic acid and linoleic monoepoxides have transient uncoupling effects, whereas the primary mechanism of toxicity for linoleic acid diols in this model is inhibition of the electron transport chain.

The role of methyl-linoleic acid epoxide and diol metabolites in the amplified toxicity of linoleic acid and polychlorinated biphenyls to vascular endothelial cells

Selected dietary lipids may increase the atherogenic effects of environmental chemicals, such as polychlorinated biphenyls (PCBs), by cross-amplifying mechanisms leading to dysfunction of the vascular endothelium. We have shown previously that the omega-6 parent fatty acid, linoleic acid, or 3,3',4,4'-tetrachlorobiphenyl (PCB 77), an aryl hydrocarbon (Ah) receptor agonist, independently can cause disruption of endothelial barrier function. Furthermore, cellular enrichment with linoleic acid can amplify PCB-induced endothelial cell dysfunction. We hypothesize that the amplified toxicity of linoleic acid and PCBs to endothelial cells could be mediated in part by cytotoxic epoxide metabolites of linoleic acid called leukotoxins (LTX) or their diol derivatives (LTXD). Exposure to LTXD resulted in a dose-dependent increase in albumin transfer across endothelial cell monolayers, whereas this disruption of endothelial barrier function was observed only at a high concentration of LTX. Pretreatment with the cytosolic epoxide hydrolase inhibitor 1-cyclohexyl-3-dodecyl urea partially protected against the observed LTX-induced endothelial dysfunction. Endothelial cell activation mediated by LTX and/or LTXD also enhanced nuclear translocation of the transcription factor NF-kappa B and gene expression of the inflammatory cytokine IL-6. Inhibiting cytosolic epoxide hydrolase decreased the LTX-mediated induction of both NF-kappa B and the IL-6 gene, whereas the antioxidant vitamin E did not block LTX-induced endothelial cell activation. Most importantly, inhibition of cytosolic epoxide hydrolase blocked both linoleic acid-induced cytotoxicity, as well as the additive toxicity of linoleic acid plus PCB 77 to endothelial cells. Interestingly, cellular uptake and accumulation of linoleic acid was markedly enhanced in the presence of PCB 77. These data suggest that cytotoxic epoxide metabolites of linoleic acid play a critical role in linoleic acid-induced endothelial cell dysfunction. Furthermore, the severe toxicity of PCBs in the presence of linoleic acid may be due in part to the generation of epoxide and diol metabolites. These findings have implications in understanding interactive mechanisms of how dietary fats can modulate dysfunction of the vascular endothelium mediated by certain environmental contaminants.

Analysis of the cytotoxic properties of linoleic acid metabolites produced by renal and hepatic P450s

Cytochrome P450 epoxidation of linoleic acid produces biologically active metabolites which have been associated with many pathological conditions that often lead to acute renal failure. In the present study, we evaluated the ability of specific cytochrome P450s to produce linoleic acid monoepoxides. We then tested the cytotoxic properties of linoleic acid, linoleic acid monoepoxides, and corresponding diols in a rabbit renal proximal tubule model. CYP1A2, CYP2E1, CYP2J2, CYP2J3, CYP2J5, and CYP2J9 metabolized linoleic acid at rates comparable to arachidonic acid and produced linoleic acid monoepoxides as major products. Cytotoxicity studies showed that linoleic acid, linoleic acid monoepoxides, and corresponding diols are toxic at pathologically relevant concentrations (100-500 microM). Concentration-dependent studies showed that linoleic acid and linoleic acid monoepoxides are the most toxic and induce mitochondrial dysfunction prior to cell death. Cytoprotectants known to block cell death associated with mitochondrial dysfunction and oxidative stress did not prevent cell death induced by linoleic acid and linoleic acid monoepoxides. This study shows that P450s in the CYP1 and CYP2 gene families metabolize linoleic acid to linoleic acid monoepoxides and that the monoepoxides, as well as linoleic acid, disrupt mitochondrial function without causing oxidative stress.

Linoleic acid cytotoxicity to bovine lens epithelial cells: influence of albumin on linoleic acid uptake and cytotoxicity

The high cytotoxicity of linoleic acid (LA) to cultured bovine lens epithelial cells is correlated with high uptake rates for the fatty acid (FA). Both, LA uptake and LA cytotoxicity strongly increase with the increasing LA-to-albumin molar ratio in the culture medium. Cellular uptake and cytotoxicity of LA can be competitively inhibited with the noncytotoxic palmitic acid. The findings may be of interest in view of the low albumin concentration in aqueous humor, resulting in extremely low buffering capacities for free FAs including LA, oleic acid and other cytotoxic cis-unsaturated free FAs, which are strongly raised in pathological situations like diabetes mellitus.

Role of 1,N2-propanodeoxyguanosine adducts as endogenous DNA lesions in rodents and humans

Results obtained in a number of studies in vitro and in vivo support the hypothesis that short- and long-chain enals and their epoxides derived from oxidized polyunsaturated fatty acids are potential endogenous sources of cyclic propano and etheno DNA adducts. We previously reviewed the evidence from some of these studies. Here, we describe the results of our more recent studies on the role of 1,N2-propanodeoxyguanosine adducts as endogenous DNA lesions. These studies include: the detection of distinct patterns of such adducts in various tissues of different species; the detection of long-chain trans-4-hydroxynonenal-derived deoxyguanosine adducts in vivo; the specificity of the formation of enal-derived propano adducts from omega-3 and omega-6 polyunsaturated fatty acids; and the detection of acrolein- and crotonaldehyde-derived adducts in human oral tissue DNA and their increased levels in smokers. Taken together, these studies further strengthen the hypothesis that enals produced by lipid peroxidation are the primary source for cyclic propano adducts in vivo, but these results cannot rule out the possible contribution of environmental and other sources. The mutagenicity of enals and their epoxides and the results of site-specific mutagenesis studies indicate that the cyclic adducts are potential promutagenic lesions; however, only circumstantial evidence is currently available for their role in carcinogenesis.

Toxicological evaluation of dietary conjugated linoleic acid in male Fischer 344 rats

To assess the toxicity of conjugated linoleic acid (CLA) after an extended feeding period, 40 male Fischer 344 rats were given either a basal diet (control) or the same diet supplemented with 1.5% CLA. During the 36-wk study, food disappearance, body weights, and cageside examinations were determined weekly and were found to be unaffected by CLA treatment. On termination, 15 major organs from 10 animals in each treatment group were excised, weighed, and prepared for histopathological evaluation. Results indicated no treatment-related effects. Likewise, haematological analysis of collected cardiac blood did not reveal any significant difference. The average daily intake of CLA by rats in this study was 80-fold and 50-fold greater than the estimated 50th and 90th percentile daily intakes, respectively, for teenage boys. Hence, results from this study indicate a lack of toxicity and support the potential determination for the GRAS status of CLA.

Effect of linoleic acid, linoleic acid anilide, and arachidonic acid on the expression of adhesion molecules on human neutrophils

The effects of linoleic acid, linoleic acid anilide, and arachidonic acid on the expression of CD11b/ CD18, CD11c/CD18 integrins and L-selectin on human neutrophils were studied by flow cytometry in a whole blood assay. None of these compounds had any effect on the basal expression of CD11b, CD11c, or L-selectin in the concentration range of 20-100 microM. However, linoleic acid at a concentration of 1000 microM slightly up-regulated CD11b and CD11c by a factor of 2.1 and 1.7, respectively. Linoleic acid, linoleic acid anilide, and arachidonic acid did not affect the formyl-methionyl-leucyl-phenylalanine induced up-regulation of CD11b or CD11c. However, linoleic acid and linoleic acid anilide slightly inhibited the phorbol myristate acetate (PMA)-induced expression of CD11b, which was decreased by 27 and 21% at concentrations of 100 and 1000 microM, respectively. Likewise, arachidonic acid at 40 microM inhibited the PMA-induced expression of CD11b by 19%. Our results suggest that linoleic acid, linoleic acid anilide, and arachidonic acid do not dramatically affect the expression of leukocyte adhesion molecules in a whole blood assay.