Conjugated linoleic acid isomers in mitochondria: evidence for an alteration of fatty acid oxidation

Cannabinoid-1 Receptor Antagonism Improves Glycemic Control and Increases Energy Expenditure Through Sirtuin-1/Mechanistic Target of Rapamycin Complex 2 and 5'Adenosine Monophosphate-Activated Protein Kinase Signaling

Endocannabinoids promote energy conservation in obesity, whereas cannabinoid-1 receptor (CB₁ R) blockade reverses body weight gain and insulin resistance and increases energy expenditure. Here we investigated the molecular mechanisms of the catabolic effects of CB₁ R blockade in the liver. Exposure of primary mouse hepatocytes and HepG2 cells to the CB₁ R agonist arachidonyl-2'-chloroethylamide inhibited the expression of Sirtuin-1 (Sirt1) and Rictor, a component of mechanistic target of rapamycin complex 2 (mTORC2) and suppressed insulin-induced Akt phosphorylation at serine 473. These effects were reversed by peripheral CB₁ R antagonist JD5037 in control hepatocytes but not in hepatocytes deficient in Sirt1 and/or Rictor, indicating that these two proteins are required for the CB₁ R-mediated inhibition of insulin signaling. Feeding C57BL/6J mice a high-fat diet (HFD) inhibited hepatic Sirt1/mTORC2/Akt signaling, and the inhibition was reversed by rimonabant or JD5037 in wild-type but not liver-specific Sirt1^-/- (Sirt1-LKO) mice, to levels observed in hepatocyte-specific CB₁ R^-/- mice. A similar attenuation of hyperglycemia and hyperinsulinemia in wild-type mice with obesity but not in Sirt1-LKO mice could be attributed to insufficient reversal of HFD-induced mitochondrial reactive oxygen species generation in peripheral tissues in the latter. In contrast, JD5037 treatment was equally effective in HFD-fed wild-type and Sirt1-LKO mice in reducing hepatic steatosis, increasing fatty acid β-oxidation, and activating 5'adenosine monophosphate-activated protein kinase (AMPK) through liver kinase B1 (LKB1), resulting in a similar increase in total energy expenditure in the two strains. Conclusion: Peripheral CB₁ R blockade in mice with obesity improves glycemic control through the hepatic Sirt1/mTORC2/Akt pathway, whereas it increases fatty acid oxidation through LKB1/AMPK signaling.

Conjugated linoleic acid and nitrite attenuate mitochondrial dysfunction during myocardial ischemia

Cardiovascular health is influenced by dietary composition and the western diet is composed of varying types/amounts of fat. Conjugated linoleic acid (cLA) is an abundant dietary unsaturated fatty acid associated with health benefits but its biological signaling is not well understood. Nitrite is enriched in vegetables within the diet and can impact signaling of unsaturated fatty acids; however, its role on cLA signaling is not well understood. Elucidating how nitrite may impact the biological signaling of cLA is important due to the dietary consumption of both cLA and nitrite in the western diet. Since co-administration of cLA and nitrite results in cardioprotection during myocardial infarction (MI), it was hypothesized that cLA and nitrite may affect cardiac mitochondrial respiratory function and complex activity in MI. C57BL/6J mice were treated with cLA and nitrite for either 10 or 13days, where MI was induced on day 3. Following treatment, respiration and complex activity were measured. Among the major findings of this study, cLA treatment (10days) decreases state 3 respiration in vivo. Following MI, nitrite alone and in combination with cLA attenuates increased state 3 respiration and decreases hydrogen peroxide levels. Further, nitrite and cLA co-treatment attenuates increased complex III activity after MI. These results suggest that cLA, nitrite and the combination significantly alter cardiac mitochondrial respiratory and electron transport chain activity in vivo and following MI. Overall, the daily consumption of cLA and nitrite in the diet can have diverse cardiovascular implications, some of which occur at the mitochondrial level.

10E,12Z-conjugated linoleic acid impairs adipocyte triglyceride storage by enhancing fatty acid oxidation, lipolysis, and mitochondrial reactive oxygen species

Conjugated linoleic acid (CLA) is a naturally occurring dietary trans fatty acid found in food from ruminant sources. One specific CLA isomer, 10E,12Z-CLA, has been associated with health benefits, such as reduced adiposity, while simultaneously promoting deleterious effects, such as systemic inflammation, insulin resistance, and dyslipidemia. The precise mechanisms by which 10E,12Z-CLA exerts these effects remain unknown. Despite potential health consequences, CLA continues to be advertised as a natural weight loss supplement, warranting further studies on its effects on lipid metabolism. We hypothesized that 10E,12Z-CLA impairs lipid storage in adipose tissue by altering the lipid metabolism of white adipocytes. We demonstrate that 10E,12Z-CLA reduced triglyceride storage due to enhanced fatty acid oxidation and lipolysis, coupled with diminished glucose uptake and utilization in cultured adipocytes. This switch to lipid utilization was accompanied by a potent proinflammatory response, including the generation of cytokines, monocyte chemotactic factors, and mitochondrial superoxide. Disrupting fatty acid oxidation restored glucose utilization and attenuated the inflammatory response to 10E,12Z-CLA, suggesting that fatty acid oxidation is critical in promoting this phenotype. With further investigation into the biochemical pathways involved in adipocyte responses to 10E,12Z-CLA, we can discern more information about its safety and efficacy in promoting weight loss.

Shc proteins influence the activities of enzymes involved in fatty acid oxidation and ketogenesis

OBJECTIVES

ShcKO mice have low body fat and resist weight gain on a high fat diet, indicating that Shc proteins may influence enzymes involved in β-oxidation. To investigate this idea, the activities of β-oxidation and ketone body metabolism enzymes were measured.

METHODS

The activities of β-oxidation enzymes (acyl-CoA dehydrogenase, 3-hydroxyacyl-CoA dehydrogenase and ketoacyl-CoA thiolase) in liver and hindlimb skeletal muscle, ketolytic enzymes (acetoacetyl-CoA thiolase, β-hydroxybutyrate dehydrogenase and 3-oxoacid-CoA transferase) in skeletal muscle, and ketogenic enzymes (acetoacetyl-CoA thiolase and β-hydroxybutyrate dehydrogenase) in liver were measured from wild-type and ShcKO mice.

RESULTS

The activities of β-oxidation enzymes were increased (P<.05) in the ShcKO compared to wild-type mice in the fasted but not the fed state. In contrast, no uniform increases in the ketolytic enzyme activities were observed between ShcKO and wild-type mice. In liver, the activities of ketogenic enzymes were increased (P<.05) in ShcKO compared to wild-type mice in both the fed and fasted states. Levels of phosphorylated hormone sensitive lipase from adipocytes were also increased (P<.05) in fasted ShcKO mice.

CONCLUSION

These studies indicate that the low Shc levels in ShcKO mice result in increased liver and muscle β-oxidation enzyme activities in response to fasting and induce chronic increases in the activity of liver ketogenic enzymes. Decreases in the level of Shc proteins should be considered as possible contributors to the increase in activity of fatty acid oxidation enzymes in response to physiological conditions which increase reliance on fatty acids as a source of energy.

Oncogene-induced senescence results in marked metabolic and bioenergetic alterations

Oncogene-induced senescence (OIS) is characterized by permanent growth arrest and the acquisition of a secretory, pro-inflammatory state. Increasingly, OIS is viewed as an important barrier to tumorgenesis. Surprisingly, relatively little is known about the metabolic changes that accompany and therefore may contribute to OIS. Here, we have performed a metabolomic and bioenergetic analysis of Ras-induced senescence. Profiling approximately 300 different intracellular metabolites reveals that cells that have undergone OIS develop a unique metabolic signature that differs markedly from cells undergoing replicative senescence. A number of lipid metabolites appear uniquely increased in OIS cells, including a marked increase in the level of certain intracellular long chain fatty acids. Functional studies reveal that this alteration in the metabolome reflects substantial changes in overall lipid metabolism. In particular, Ras-induced senescent cells manifest a decline in lipid synthesis and a significant increase in fatty acid oxidation. Increased fatty acid oxidation results in an unexpectedly high rate of basal oxygen consumption in cells that have undergone OIS. Pharmacological or genetic inhibition of carnitine palmitoyltransferase 1, the rate-limiting step in mitochondrial fatty acid oxidation, restores a pre-senescent metabolic rate and, surprisingly, selectively inhibits the secretory, pro-inflammatory state that accompanies OIS. Thus, Ras-induced senescent cells demonstrate profound alterations in their metabolic and bioenergetic profiles, particularly with regards to the levels, synthesis and oxidation of free fatty acids. Furthermore, the inflammatory phenotype that accompanies OIS appears to be related to these underlying changes in cellular metabolism.

Antagonism of peripheral hepatic cannabinoid receptor-1 improves liver lipid metabolism in mice: evidence from cultured explants

It is well established that inactivation of the central endocannabinoid system (ECS) through antagonism of cannabinoid receptor 1 (CB1R) reduces food intake and improves several pathological features associated with obesity, such as dyslipidemia and liver steatosis. Nevertheless, recent data indicate that inactivation of peripheral CB1R could also be directly involved in the control of lipid metabolism independently of central CB1R. To further investigate this notion, we tested the direct effect of the specific CB1R antagonist, SR141716, on hepatic carbohydrate and lipid metabolism using cultured liver slices. CB1R messenger RNA expression was strongly decreased by SR141716, whereas it was increased by the CB1R agonist, arachidonic acid N-hydroxyethylamide (AEA), indicating the effectiveness of treatments in modulating ECS activity in liver explants both from lean or ob/ob mice. The measurement of O(2) consumption revealed that SR141716 increased carbohydrate or fatty acid utilization, according to the cellular hormonal environment. In line with this, SR141716 stimulated ß-oxidation activity, and the role of CB1R in regulating this pathway was particularly emphasized when ECS was hyperactivated by AEA and in ob/ob tissue. SR141716 also improved carbohydrate and lipid metabolism, blunting the AEA-induced increase in gene expression of proteins related to lipogenesis. In addition, we showed that SR141716 induced cholesterol de novo synthesis and high-density lipoprotein uptake, revealing a relationship between CB1R and cholesterol metabolism.

CONCLUSION

These data suggest that blocking hepatic CB1R improves both carbohydrate and lipid metabolism and confirm that peripheral CB1R should be considered as a promising target to reduce cardiometabolic risk in obesity.

CLA-enriched diet containing t10,c12-CLA alters bile acid homeostasis and increases the risk of cholelithiasis in mice

Mice fed a mixture of CLA containing t10,c12-CLA lose fat mass and develop hyperinsulinemia and hepatic steatosis due to an accumulation of TG and cholesterol. Because cholesterol is the precursor in bile acid (BA) synthesis, we investigated whether t10,c12-CLA alters BA metabolism. In Expt. 1, female C57Bl/6J mice were fed a standard diet for 28 d supplemented with a CLA mixture (1 g/100 g) or not (controls). In Expt. 2, the feeding period was reduced to 4, 6, and 10 d. In Expt. 3, mice were fed a diet supplemented with linoleic acid, c9,t11-CLA, or t10,c12-CLA (0.4 g/100 g) for 28 d. In Expt. 1, the BA pool size was greater in CLA-fed mice than in controls and the entero-hepatic circulation of BA was altered due to greater BA synthesis and ileal reclamation. This resulted from higher hepatic cholesterol 7α-hydroxylase (CYP7A1) and ileal apical sodium BA transporter expressions in CLA-fed mice. Furthermore, hepatic Na(+)/taurocholate co-transporting polypeptide (NTCP) (-52%) and bile salt export pump (BSEP) (-77%) protein levels were lower in CLA-fed mice than in controls, leading to a greater accumulation of BA in the plasma (+500%); also, the cholesterol saturation index and the concentration of hydrophobic BA in the bile were greater in CLA-fed mice, changes associated with the presence of cholesterol crystals. Expt. 2 suggests that CLA-mediated changes were caused by hyperinsulinemia, which occurred after 6 d of the CLA diet before NTCP and BSEP mRNA downregulation (10 d). Expt. 3 demonstrated that only t10,c12-CLA altered NTCP and BSEP mRNA levels. In conclusion, t10,c12-CLA alters BA homeostasis and increases the risk of cholelithiasis in mice.

Vaccenic and elaidic acid equally esterify into triacylglycerols, but differently into phospholipids of fed rat liver cells

Elaidic acid (trans-9-C₁₈:₁ or trans-9) is assumed to exert atherogenic effects due to its double bond configuration. The possibility that trans-9 and vaccenic acid (trans-11-C₁₈:₁ or trans-11), its positional isomer, were biochemically equivalent and interchangeable compounds, was investigated by reference to their cis-isomers through esterification-related activities using rat liver cells and subcellular fractions. In hepatocytes, both trans-C₁₈:₁ were incorporated to the same extent in triacylglycerols, but trans-9 was more esterified than trans-11 into phospholipids (P < 0.05). Glycerol-3-phosphate acyltransferase activity in microsomes was lower with trans-11 than with trans-9, while this activity in mitochondria was ~40% greater with trans-11 than with trans-9 (P < 0.05). Activity of 2-lysophosphatidic acid acyltransferase in microsomes was of comparable extent with both trans isomers, but activity of 2-lysophosphatidylcholine acyltransferase was significantly greater with trans-9 than with trans-11 at P < 0.01. Lipoproteins secreted by hepatocytes reached equivalent levels in the presence of any isomers, but triacylglycerol production was more elevated with trans-11 than with trans-9 at P < 0.05. Cholesterol efflux from previously labelled hepatocytes was lower with trans-11 than with trans-9. When these cells were exposed to either trans-C₁₈:₁, the gene expression of proteins involved in fatty acid esterification and lipoprotein synthesis was unaffected, which indicates that the biochemical differences essentially depended on enzyme/substrate affinities. On the whole, vaccenic and elaidic acid were shown to incorporate cell phospholipids unequally, at least in vitro, which suggests they can differently affect lipid metabolic pathways in normal cells.

Comparison of postprandial oleic acid, 9c,11t CLA and 10t,12c CLA oxidation in healthy moderately overweight subjects

Few studies report the individual effect of 9c,11t- and 10t,12c-CLA on human energy metabolism. We compared the postprandial oxidative metabolism of 9c,11t- and 10t,12c-CLA and oleic acid (9c-18:1) in 22 healthy moderately overweight volunteers. After 24 weeks supplementation with 9c,11t-, 10t,12c-CLA or 9c-18:1 (3 g/day), subjects consumed a single oral bolus of the appropriate [1-(13)C]-labeled fatty acid. 8 h post-dose, cumulative oxidation was similar for 9c-18:1 and 10t,12c (P = 0.66), but significantly higher for 9c,11t (P < 0.01).

Dissimilar properties of vaccenic versus elaidic acid in beta-oxidation activities and gene regulation in rat liver cells

Vaccenic acid (trans-11-C(18:1)) chemically resembles elaidic acid (trans-9-C(18:1)) which is assumed to increase the risk of cardiovascular diseases, and thus could exert similar effects. Possible different oxidation rates of vaccenic versus elaidic acid were checked in muscles and liver, and through related gene expression in normal rat liver cells. In hepatic mitochondria, carnitine palmitoyltransferase (CPT) I exhibited comparable activity rates with both trans-isomers. CPT II activity was 30% greater (P < 0.05) with vaccenic than with elaidic acid as nonesterified fatty acids (NEFAs) or acyl-CoAs. Activity of the first beta-oxidation step was similar between the isomers in all the tissue slices and liver extracts assayed. Respiration rates were comparable with both trans-isomers as NEFAs in various liver extracts, but were 30% greater (P < 0.05) with vaccenoyl-CoA than with elaidoyl-CoA in liver mitochondria. Vaccenic acid was oxidised 25% more (P < 0.05) by liver peroxisomes than elaidic acid. In hepatocytes cultured with trans- and corresponding cis-C(18:1) isomers, gene expression of CPT I, hydroxyacyl-CoA dehydrogenase and hydroxymethylglutaryl-CoA synthase was at least 100% increased (P < 0.05), but was unchanged with vaccenic acid, relative to controls. In conclusion, the position and geometry of the double bonds in acyl chains are suggested to confer on vaccenic and elaidic acid specific biochemical properties that might differently affect their fates in tissues.

Metabolism and actions of conjugated linoleic acids on atherosclerosis-related events in vascular endothelial cells and smooth muscle cells

Conjugated linoleic acids (CLAs) are biologically highly active lipid compounds that have attracted great scientific interest due to their ability to cause either inhibition of atherosclerotic plaque development or even regression of pre-established atherosclerotic plaques in mice, hamsters and rabbits. The underlying mechanisms of action, however, are only poorly understood. Since cell culture experiments are appropriate to gain insight into the mechanisms of action of a compound, the present review summarizes data from cell culture studies about the metabolism and the actions of CLAs on atherosclerosis-related events in endothelial cells (ECs) and smooth muscle cells (SMCs), which are important cells contributing to atherosclerotic lesion development. Based on these studies, it can be concluded that CLAs exert several beneficial actions including inhibition of inflammatory and vasoactive mediator release from ECs and SMCs, which may help explain the anti-atherogenic effect of CLAs observed in vivo. The observation that significant levels of CLA metabolites, which have been reported to have significant biological activities, are well detectable in ECs and SMCs indicates that the anti-atherogenic effects observed with CLAs are presumably mediated not only by CLAs themselves but also by their metabolites.

Conjugated linoleic acid isomers: differences in metabolism and biological effects

The term conjugated linoleic acid (CLA) refers to a mixture of linoleic acid positional and geometric isomers, characterized by having conjugated double bonds, not separated by a methylene group as in linoleic acid. CLA isomers appear as a minor component of the lipid fraction, found mainly in meat and dairy products from cows and sheep. The most abundant isomer is cis-9,trans-11, which represents up to 80% of total CLA in food. These isomers are metabolized in the body through different metabolic pathways, but important differences, that can have physiological consequences, are observed between the two main isomers. The trans-10,cis-12 isomer is more efficiently oxidized than the cis-9,trans-11 isomer, due to the position of its double bounds. Interest in CLA arose in its anticarcinogenic action but there is an increasing amount of specific scientific literature concerning the biological effects and properties of CLA. Numerous biological effects of CLA are due to the separate action of the most studied isomers, cis-9,trans-11 and trans-10,cis-12. It is also likely that some effects are induced and/or enhanced by these isomers acting synergistically. Although the cis-9,trans-11 isomer is mainly responsible for the anticarcinogenic effect, the trans-10,cis-12 isomer reduces body fat and it is referred as the most effective isomer affecting blood lipids. As far as insulin function is concerned, both isomers seem to be responsible for insulin resistance in humans. Finally, with regard to the immune system it is not clear whether individual isomers of CLA could act similarly or differently.

Concentration-dependent antioxidant activities of conjugated linoleic acid and α-tocopherol in corn oil

BACKGROUND

Antioxidants prevent rancidity (lipid peroxidation) and natural antioxidants, e.g., α-tocopherol, likely provide additional value to oil-based food products because of their health benefits. Conjugated linoleic acid (CLA) has potential health benefits and may exhibit antioxidant properties. The main aim of this study was to compare the antioxidant efficacy of α-tocopherol, trans-10, cis-12-CLA and cis-9, trans-11-CLA (in graded concentrations) added to antioxidant-stripped corn oil.

RESULTS

As compared to α-tocopherol, both CLA isomers displayed significant inhibition of corn oil lipid peroxidation induced by copper. Inhibition of thiobarbituric acid reactive substances (TBARS) were CLA concentration dependent for both isomers but with significant inhibition occurring at 0.1 and 1 ppm of CLA isomers or α-tocopherol, respectively (P < 0.05). Graded concentrations of α-tocopherol, and for both CLA isomers and time, had significant effects on TBARS formation (P < 0.0001). There were significant effects in interactions between graded concentrations and time for both CLA isomers (P < 0.0001) but not for α-tocopherol (P > 0.05).

CONCLUSION

CLA compounds could serve as useful food antioxidants and provide additional value because of their potential bioactivity in disease prevention. Copyright © 2007 Society of Chemical Industry.

Metabolism and short-term metabolic effects of conjugated linoleic acids in rat hepatocytes

Metabolic fate and short-term effects of a 1:1 mixture of cis-9,trans-11 and trans-10,cis-12-conjugated linoleic acids (CLA), compared to linoleic acid (LA), on lipid metabolism was investigated in rat liver. In isolated mitochondria CLA-CoA were poorer substrates than LA-CoA for carnitine palmitoyltransferase-I (CPT-I) activity. However, in digitonin-permeabilized hepatocytes, where interactions among different metabolic pathways can be simultaneously investigated, CLA induced a remarkable stimulatory effect on CPT-I activity. This stimulation can be ascribed to a reduced malonyl-CoA level in turn due to inhibition of acetyl-CoA carboxylase (ACC) activity. The ACC/malonyl-CoA/CPT-I system can therefore represent a coordinate control by which CLA may exert effects on the partitioning of fatty acids between esterification and oxidation. Moreover, the rate of oxidation to CO2 and ketone bodies was significantly higher from CLA; peroxisomes rather than mitochondria were responsible for this difference. Interestingly, peroxisomal acyl-CoA oxidase (AOX) activity strongly increased by CLA-CoA compared to LA-CoA. CLA, metabolized by hepatocytes at a higher rate than LA, were poorer substrates for cellular and VLDL-triacylglycerol (TAG) synthesis. Overall, our results suggest that increased fatty acid oxidation with consequent decreased fatty acid availability for TAG synthesis is a potential mechanism by which CLA reduce TAG level in rat liver.

Regulation of Lipid Flux between Liver and Adipose Tissue during Transient Hepatic Steatosis in Carnitine-depleted Rats

Rats with carnitine deficiency due to trimethylhydrazinium propionate (mildronate) administered at 80 mg/100 g body weight per day for 10 days developed liver steatosis only upon fasting. This study aimed to determine whether the transient steatosis resulted from triglyceride accumulation due to the amount of fatty acids preserved through impaired fatty acid oxidation and/or from up-regulation of lipid exchange between liver and adipose tissue. In liver, mildronate decreased the carnitine content by approximately 13-fold and, in fasted rats, lowered the palmitate oxidation rate by 50% in the perfused organ, increased 9-fold the triglyceride content, and doubled the hepatic very low density lipoprotein secretion rate. Concomitantly, triglyceridemia was 13-fold greater than in controls. Hepatic carnitine palmitoyltransferase I activity and palmitate oxidation capacities measured in vitro were increased after treatment. Gene expression of hepatic proteins involved in fatty acid oxidation, triglyceride formation, and lipid uptake were all increased and were associated with increased hepatic free fatty acid content in treated rats. In periepididymal adipose tissue, mildronate markedly increased lipoprotein lipase and hormone-sensitive lipase activities in fed and fasted rats, respectively. On refeeding, carnitine-depleted rats exhibited a rapid decrease in blood triglycerides and free fatty acids, then after approximately 2 h, a marked drop of liver triglycerides and a progressive decrease in liver free fatty acids. Data show that up-regulation of liver activities, peripheral lipolysis, and lipoprotein lipase activity were likely essential factors for excess fat deposit and release alternately occurring in liver and adipose tissue of carnitine-depleted rats during the fed/fasted transition.

Dietary trans 10, cis 12-conjugated linoleic acid reduces the expression of fatty acid oxidation and drug detoxification enzymes in mouse liver

Mice fed diets containing trans 10, cis 12 (t10, c12)-conjugated linoleic acid (CLA) develop fatty livers and the role of the hepatic fatty acid oxidation enzymes in this development is not well defined. We examined the effects of dietary cis 9, trans 11-CLA (c9, t11-CLA) and t10, c12-CLA on the expression of hepatic genes for fatty acid metabolism. Female mice, 8 weeks old, (six animals per group) were fed either a control diet or diets supplemented with 0.5% c9, t11- or c12-CLA for 8 weeks. DNA microarray analysis showed that t10, c12-CLA increased the expression of 278 hepatic genes and decreased those of 121 genes (>2 fold); c9, t11-CLA increased expression of twenty-two genes and decreased those of nine. Real-time PCR confirmed that t10, c12-CLA reduced by the expression of fatty acid oxidation genes including flavin monooxygenase (FMO)-3 95%, cytochrome P450 (cyt p450) 69%, carnitine palmitoyl transferase 1a 77%, acetyl CoA oxidase (ACOX) 50% and PPARalpha 65%: it increased the expression of fatty acid synthase by 3.5-fold (P<0.05 for all genes, except ACOX P=0.08). It also reduced the enzymatic activity of hepatic microsomal FMO by 40% and the FMO3 specific protein by 67%. c9, t11-CLA reduced FMO3 and cyt P450 expression by 61% (P=0.001) and 38% (P=0.06) and increased steoryl CoA desaturase transcription by 5.9-fold (P=0.07). Both decreased fatty acid oxidation and increased fatty acid synthesis seem to contribute to the CLA-induced fatty liver. Since FMO and cyt P450 are also involved in drug detoxification, suppression of the transcription of these genes by CLA may have other health consequences besides development of fatty liver.

Effects of conjugated linoleic acid (CLA) isomers on oxygen diffusion-concentration products in liposomes and phospholipid solutions

Conjugated linoleic acids (CLAs) are a group of octadecadienoic acids (18:2) that are naturally present in food products and may have beneficial health effects. Liposomes and ethanol solutions were prepared by mixing synthetic phosphatidylcholines (PCs) with c9,t11-CLA, t10,c12-CLA, and linoleic acid (LA) in the sn-2 position into natural PCs from soybean, egg yolk, rat brain, and rat heart at 5 mol %. The oxygen diffusion-concentration products were measured using electron spin resonance spin-label oximetry methods. Individual synthetic PCs, the phospholipid matrix, and the tested lipid systems all exhibited influence on oxygen diffusion-concentration products during lipid peroxidation. Incorporating 5 mol % PC(c9,t11-CLA) into soy and egg yolk PC increased oxygen consumption in liposome suspensions while it was decreased in rat heart and brain PCs. On the other hand, PC(t10,c12-CLA) increased oxygen consumption in mixtures with egg yolk and rat heart PC but decreased it in soybean and rat brain PC. By comparison, PC(LA) decreased oxygen consumption in every case. In ethanol solutions, all of the synthetic PCs suppressed the capacity to generate peroxide radicals in the order of LA > c9,t11-CLA > t10,c12-CLA. In addition, PCs containing individual CLA isomers and LA differed in their capacities to react with and quench DPPH radicals in both ethanol solution and liposome, suggesting differences between CLA isomers and LA in DPPH radical-fatty acid interactions. Incorporation of CLA isomers and LA into dimyristyl-PC reduced the phase transition temperature from 23.6 to 23.1 and 23.3 degrees C, respectively. The results of this study provide evidence that the behavior of CLA isomers differs in the microenvironment of membranes possibly due to structural differences that affect the permeability of membranes to oxygen and lipid peroxidation.

Distribution of polyunsaturated fatty acids including conjugated linoleic acids in total and subcellular fractions from healthy and cancerous parts of human kidneys

Differences in the FA composition of subcellular fractions from healthy and cancerous kidney tissues from the same patients were examined. Only minor differences in CLA content were found between the healthy and the cancerous tissue portions. Regarding the distribution pattern, CLA incorporation into nuclei and cytosol was significantly higher than incorporation into plasma membranes and mitochondria, which could be correlated to the neutral lipid content of these fractions. The subcellular distribution pattern of CLA was similar to that observed with monounsaturated FA but unlike that found with 18:2n-6, which underlines the different physiological properties of CLA and 18:2n-6. Because PUFA have been suggested to have an effect on cancer risk, the contents of n-3 and n-6 PUFA were determined in kidney and renal cell carcinoma (RCC). The 18:2n-6 content and delta5 desaturase activity were significantly lower, and the 18:3n-6, 20:3n-6, and 20:5n-3 contents and delta6 desaturase activity were significantly higher in RCC than in healthy renal tissue, indicating a changed PUFA metabolism in RCC. Previous research has suggested that CLA inhibits the elongation and desaturation of 18:2n-6 into 20:4n-6. In that case, one might speculate that a diet enriched in CLA would be a useful tool in preventing RCC. However, the involvement of CLA in preventing renal cancer could not be demonstrated definitively from the design of this experiment. Further understanding of the cause and/or consequence of the difference in FA metabolism may lead to a better understanding of RCC.

Distribution of conjugated linoleic acid in total and subcellular fractions from normal and cancerous parts of human testes

The objective of the present study was to examine differences in the fatty acid composition of subcellular fractions from normal and cancerous parts of human testes. The conjugated linoleic acid (CLA) content was significantly higher in total testicular carcinoma (TC), but significantly lower in the mitochondrial fraction of TC in comparison to normal testicular tissue. The subcellular distribution pattern of CLA was similar to that of monounsaturated fatty acids, but different to that of 18:2n-6 (linoleic acid), underlining the different physiological properties of CLA and 18 : 2n-6. Because polyunsaturated fatty acids (PUFAs) have been suggested to have an effect on cancer risk and previous research has found that CLA inhibits the metabolism of 18 : 2n-6 into 20 : 4n-6, the contents of n-6 and n-3 PUFAs were determined. Significant differences were observed for 18 : 2n-6, 18 : 3n-3, 20 : 5n-3, and 22 : 6n-3, with 18 : 2n-6, 18 : 3n-3, and 20 : 5n-3 contents being higher and 22 : 6n-3 content being lower in TC than in normal testicular tissue. These results indicate a changed availability of substrates for the cyclooxygenase (COX) or lipooxygenase (LOX) pathways generating eicosanoids. Although not statistically significant, the reduced content of 20 : 4n-6 shown in this study might be due to an increased metabolism of this fatty acid into eicosanoids.

Analysis of the contribution of the β-oxidation auxiliary enzymes in the degradation of the dietary conjugated linoleic acid 9-cis-11-trans-octadecadienoic acid in the peroxisomes of Saccharomyces cerevisiae

Beta-oxidation of the conjugated linoleic acid 9-cis,11-trans-octadecadienoic acid (rumenic acid) was analyzed in vivo in Saccharomyces cerevisiae by monitoring polyhydroxyalkanoate production in the peroxisome. Polyhydroxyalkanoate is synthesized by the polymerization of the beta-oxidation intermediates 3-hydroxyacyl-CoAs via a bacterial polyhydroxyalkanoate synthase targeted to the peroxisome. The amount of polyhydroxyalkanaote synthesized from the degradation of rumenic acid was found to be similar to the amount synthesized from the degradation of 10-trans,12-cis-octadecadienoic acid, oleic acid or 10-cis-heptadecenoic acid. Furthermore, the degradation of 10-cis-heptadecenoic acid was found to be unaffected by the presence of rumenic acid in the media. Efficient degradation of rumenic acid was found to be independent of the Delta(3,5),Delta(2,4)-dienoyl-CoA isomerase but instead relied on the presence of Delta(3),Delta(2)-enoyl-CoA isomerase activity. The presence of the unsaturated monomer 3-hydroxydodecenoic acid in polyhydroxyalkanoate derived from rumenic acid degradation was found to be dependent on the presence of a Delta(3),Delta(2)-enoyl-CoA isomerase activity. Together, these data indicate that rumenic acid is mainly degraded in vivo in S. cerevisiae through a pathway requiring only the participation of the auxiliary enzymes Delta(3),Delta(2)-enoyl-CoA isomerase, along with the enzyme of the core beta-oxidation cycle.

New application of a subcellular fractionation method to kidney and testis for the determination of conjugated linoleic acid in selected cell organelles of healthy and cancerous human tissues

To clarify the mechanism of the anticarcinogenic effect of conjugated linoleic acid (CLA), its intracellular distribution needs to be determined. Subcellular fractionation using centrifugation techniques is a method that is frequently used for isolation of cell organelles from different tissues. But as the size and density of the organelles differ, the method needs to be optimised for every type of tissue. The novelty of this study is the application of a subcellular fractionation method to human healthy and cancerous renal and testicular tissue. Separation of total tissue homogenate into nuclei, cytosol, and a mixture of mitochondria and plasma membranes was achieved by differential centrifugation. As mitochondria and plasma membranes seemed to be too similar in size and weight to be separated by differential centrifugation, discontinuous density-gradient centrifugation was carried out successfully. The purity of the subcellular fractions was checked by measuring the activity of marker enzymes. All fractions were highly enriched in their corresponding marker enzyme. However, the nuclear fractions of kidney and renal cell carcinoma were slightly contaminated with mitochondria and plasma membrane fractions of all tissues with lysosomes. The fraction designated the cytosolic fraction contained not only cytosol, but also microsomes and lysosomes. The CLA contents of the subcellular fractions were in the range 0.13-0.37% of total fatty acids and were lowest in the plasma membrane fractions of all types of tissue studied. C16:0, C18:0, C18:1 c9, C18:2 n-6, and C20:4 n-6 were found to be the major fatty acids in all the subcellular fractions studied. However, marked variations in fatty acid content between subcellular fractions and between types of tissue were detectable. Because of these differences between tissues, no general statement on characteristic fatty acid profiles of single subcellular fractions is possible.

Vitamin D3?Based Conjugates for Topical Treatment of Psoriasis: Synthesis, Antiproliferative Activity, and Cutaneous Penetration Studies

PURPOSE

The goals of the experiments reported in this paper were to explore skin bioavailability and cell growth inhibitory activity of new vitamin D3-based conjugates studied as a potential drug complex for psoriasis.

METHODS

Conjugation was made between polyunsaturated fatty acids (PUFAs), such as linolenic acid or gamma-linolenic acid, and calcipotriol--a vitamin D3 analogue clinically used for topical treatment of psoriasis. These complexes were prepared by coupling the corresponding fatty acid with calcipotriol in the presence of dicyclohexyl-carbodiimide (DCC) and 4-(dimethylamino)-pyridine (DMAP) to obtain an ester bond.

RESULTS

The conjugates were capable of enhancing the penetration of the vitamin into the skin as well as inhibiting proliferation of keratinocytes in cultures. The antiproliferative activity even increased after simulating the full hydrolysis of the conjugates. In vitro skin penetration studies revealed that the conjugates penetrated into the skin at higher levels relative to calcipotriol alone. It was also demonstrated that the conjugate containing n-3 fatty acid penetrated into the skin at higher levels as compared to the conjugate containing n-6 PUFA. High-performance liquid chromatography analysis has shown that after penetration, a major portion of calcipotriol-PUFA conjugate was first converted mainly into another isomer form, presumably by transesterification, and only then it was hydrolyzed to form apparently high local concentrations of both calcipotriol and PUFA.

CONCLUSIONS

The unique biotransformation that occurred after penetration into the skin indicates that these conjugates are mutual prodrugs that are able to be bioprocessed in the skin and fully converted to the parent therapeutic agents.

Is autism a disorder of fatty acid metabolism? Possible dysfunction of mitochondrial beta-oxidation by long chain acyl-CoA dehydrogenase

Long chain acyl-CoA dehydrogenase (LCAD) has recently been shown to be the mitochondrial enzyme responsible for the beta-oxidation of branched chain and unsaturated fatty acids [Biochim. Biophys. Acta 1393 (1998) 35; Biochim. Biophys. Acta 1485 (2000) 121]. Whilst disorders of short, medium and very long chain acyl dehydrogenases are known, there is no known disorder of LCAD deficiency in humans. Experimental LCAD deficiency in mice shows an acyl-carnitine profile with prominent elevations of unsaturated fatty acid metabolites C14:1 and C14:2 [Hum. Mol. Genet. 10 (2001) 2069]. A child with autism whose acyl-carnitine profile also shows these abnormalities is presented, and it is hypothesized that the child may have LCAD deficiency. Additional metabolic abnormalities seen in this patient include alterations of TCA energy production, ammonia detoxification, reduced synthesis of omega-3 DHA, and abnormal cholesterol metabolism. These metabolic changes are also seen as secondary abnormalities in dysfunction of fatty acid beta-oxidation, and have also been reported in autism. It is hypothesized that LCAD deficiency may be a cause of autism. Similarities between metabolic disturbances in autism, and those of disorders of fatty acid beta-oxidation are discussed.

Conjugated linoleic acids, atherosclerosis, and hepatic very-low-density lipoprotein metabolism

Conjugated linoleic acids (CLAs) are isomeric forms of the 18:2 fatty acid that contain conjugated sites of unsaturation. Although CLAs are minor components of the diet, they have many reported biological activities. For nearly a decade, the potential for CLA to modify the atherosclerotic process has been examined in animal models, and studies of supplementation of the human diet with CLA were started with the anticipation that such an intervention could also reduce the risk of cardiovascular disease. Central to the hypothesis is the expectation that dietary modification could alter plasma lipid and lipoprotein metabolism toward a more cardioprotective profile. This review examines the evidence in support of the hypothesis and the mechanistic studies that lend support for a role of CLA in hepatic lipid and lipoprotein metabolism. Although there are still limited studies in strong support of a role for CLA in the reduction of early atherosclerotic lesions, there has been considerable progress in defining the mechanisms of CLA action. CLA could primarily modulate the metabolism of fatty acids in the liver. The tools are now available to examine isomer-specific effects of CLA on hepatic lipid and lipoprotein metabolism and the potential of CLA to modify hepatic gene expression patterns. Additional animal and cell culture studies will increase our understanding of these unusual fatty acids and their potential for health benefits in humans.

Hepatic steatosis is not due to impaired fatty acid oxidation capacities in C57BL/6J mice fed the conjugated trans-10,cis-12-isomer of linoleic acid

Decreased body fat mass and liver steatosis have been reported in mice fed diets containing the conjugated linoleic acid trans-10,cis-12-C18:2 (CLA2), but not in those fed diets containing cis-9,trans-11-C18:2 (CLA1). Because the decrease in fatty acid (FA) oxidation may cause fat accumulation, we questioned whether the effects of both CLAs on enzyme activities and mRNA expression were related to liver FA oxidation. To address this question, 7-wk-old male C57BL/6J mice were fed for 4 wk a diet supplemented with 1% CLA1, CLA2, or cis-9-C18:1 (control) esterified as triacylglycerols. In CLA2-fed mice, the proportions of CLA2 in the total FA of liver lipids were substantially lower than those of CLA1 in mice fed CLA1. The mitochondrial protein content per total liver was about 56% greater in CLA2-fed mice than in CLA1-fed mice and controls. Mitochondrial carnitine palmitoyltransferase I (CPT I) and carnitine-dependent palmitate oxidation activities were also significantly greater in CLA2-fed mice than in the two other groups. The amounts of malonyl-CoA per gram of liver and the sensitivity of CPT I to malonyl-CoA inhibition were greater in both groups of CLA-fed mice than in the controls. L-CPT I mRNA expression doubled in CLA2-fed mice and was 3 and 2 times greater for M-CPT I in the CLA1 and CLA2 groups, respectively, compared with controls. Peroxisomal FA oxidation-related activities and acyl-CoA oxidase mRNA expression were increased in CLA1-fed mice, and to a larger extent in CLA2-fed mice, relative to controls. These data indicate that FA oxidation capacities were increased in mice fed CLA2, but were likely depressed in vivo through malonyl-CoA inhibition.

Effects of Conjugated Linoleic Acid Isomers on Lipid Metabolism and Gluconeogenesis in Monolayer Cultures of Bovine Hepatocytes

The objective was to determine the effects of linoleic acid and different isomers of conjugated linoleic acid (CLA) at different concentrations on hepatic lipid and glucose metabolism in the bovine. Monolayer cultures of hepatocytes obtained from 7- to 10-d-old Holstein bull calves were exposed to treatments from 16 to 64 h after plating. The treatments included 1.0 mM palmitic acid plus either 0.1 or 1.0 mM of cis-9, cis-12 linoleic acid, cis-9, trans-11 CLA, or trans-10, cis-12 CLA. Metabolism of palmitic acid to cellular triacylglycerol (TAG) was decreased when media contained cis-9, trans-11 compared with trans-10, cis-12 CLA. Total cellular TAG content was increased for the CLA isomers compared to cis-9, cis-12 linoleic acid. Both CLA isomers increased palmitic acid incorporation into phospholipids, cholesterol, and media triacylglycerol compared with cis-9, cis-12 linoleic acid at a concentration of 1.0 mM. Increasing the concentration of treatment fatty acids from 0.1 to 1.0 mM decreased oxidation of palmitic acid to acid-soluble products, but no effects of fatty acids were observed. There was no treatment effect on rates of gluconeogenesis from propionic acid. Overall, CLA isomers elicited changes in palmitic acid metabolism to cellular and media triacylglycerol, and cellular phospholipids and cholesterol, but had little or no effect on other measured pathways of lipid metabolism or gluconeogenesis in bovine hepatocytes.

cis-9,trans-11 and trans-10,cis-12 CLA affect lipid metabolism differently in primary white and brown adipocytes of djungarian hamsters

We explored whether CLA isomers and other C18 FA affect (i) lipid content and FA concentrations in total adipocyte lipids, (ii) FA synthesis from glucose in TAG and phospholipids of primary brown (BAT) and white adipocytes (WAT), and (iii) mRNA expression of uncoupling protein 1 (UCP1) in primary brown adipocytes of Djungarian hamsters (Phodopus sungorus). c9,t11-CLA, oleic, linoleic, and alpha-linolenic acid increased whereas t10,c12-CLA decreased lipid accumulation in both adipocyte types. t10,c12-CLA treatment affected FA composition mainly in BAT cells. CLA incorporation into lipids, in particular c9,t11-CLA, was higher in BAT. In both cell types, t10,c12-CLA treatment reduced the incorporation of glucose 13C carbon into FA of TAG and phospholipids, whereas c9,t11-CLA, linoleic, and alpha-linolenic acid either did not influence or dose-dependently increased glucose carbon incorporation into FA. UCP1 mRNA expression was inhibited by t10,c12-CLA but increased by c9,t11-CLA, linoleic, and alpha-linolenic acid. It is concluded that c9,t11-CLA and t10,c12-CLA have distinctly different effects on lipid metabolism in primary adipocytes. The effects of c9,t11-CLA are similar to those of other unsaturated C18 FA. The opposite effects of c9,t11-CLA and t10,c12-CLA are evident in both WAT and BAT cultures; however, brown adipocytes seem to be more susceptible to CLA treatment.

Isomer-specific regulation of metabolism and PPARgamma signaling by CLA in human preadipocytes

Trans-10,cis-12 conjugated linoleic acid (CLA) has previously been shown to be the CLA isomer responsible for CLA-induced reductions in body fat in animal models, and we have shown that this isomer, but not the cis-9,trans-11 CLA isomer, specifically decreased triglyceride (TG) accumulation in primary human adipocytes in vitro. Here we investigated the mechanism behind the isomer-specific, CLA-mediated reduction in TG accumulation in differentiating human preadipocytes. Trans-10,cis-12 CLA decreased insulin-stimulated glucose uptake and oxidation, and reduced insulin-dependent glucose transporter 4 gene expression. Furthermore, trans-10,cis-12 CLA reduced oleic acid uptake and oxidation when compared with all other treatments. In parallel to CLA's effects on metabolism, trans-10,cis-12 CLA decreased, whereas cis-9,trans-11 CLA increased, the expression of peroxisome proliferator-activated receptor gamma (PPARgamma) and several of its downstream target genes when compared with vehicle controls. Transient transfections demonstrated that both CLA isomers antagonized ligand-dependent activation of PPARgamma. Collectively, trans-10,cis-12, but not cis-9, trans-11, CLA decreased glucose and lipid uptake and oxidation and preadipocyte differentiation by altering preadipocyte gene transcription in a manner that appeared to be due, in part, to decreased PPARgamma expression.