Fatty acid regulation of gene expression. Its role in fuel partitioning and insulin resistance

Fatty acid consumption and incident type 2 diabetes: an 18-year follow-up in the female E3N (Etude Epidémiologique auprès des femmes de la Mutuelle Générale de l’Education Nationale) prospective cohort study

We evaluated the association between dietary estimates of fatty acid (FA) consumption and type 2 diabetes (T2D) risk in the French E3N (Etude Epidémiologique auprès des femmes de la Mutuelle Générale de l’Education Nationale) cohort. In total, 71 334 women without diabetes at baseline were followed up from 1993 to 2011. Diabetes was identified using questionnaires and drug-reimbursement claims, and incident cases were validated. FA consumption in 1993 was estimated from a validated dietary questionnaire. Cox regression estimated hazard ratios (HR) and 95 % CI of diabetes risk, comparing the upper tertile group with the lowest. High n-3 PUFA consumption was associated with T2D even after adjustment for confounders, including other FA and BMI (HR 1·26; 95 % CI 1·13, 1·41; upper tertile compared with lowest). Upon stratification by overweight (BMI≥25 kg/m2)/non-overweight, a positive association between total PUFA consumption and T2D was observed, but it was restricted to non-overweight women (HR 1·22; 95 % CI 1·05, 1·42), whereas n-3 PUFA consumption was associated with increased T2D risk in both BMI strata (BMI<25 kg/m2: HR 1·19; 95 % CI 1·01, 1·40 and BMI≥25 kg/m2: HR 1·38; 95 % CI 1·20, 1·59). Within the n-3 PUFA, high DPA (HR 1·41; 95 % CI 1·23, 1·63) and α-linolenic acid (ALA) intakes were associated with increased T2D risk, but the effects of ALA were restricted to overweight women (HR 1·17; 95 % CI 1·01, 1·36). Within the n-6 PUFA, only arachidonic acid (AA) intake was associated with T2D risk (HR 1·49; 95 % CI 1·33, 1·66). The associations with DPA and AA persisted even after adjustment of their principal source in this cohort, the consumption of meat. The effects of PUFA are heterogeneous within the FA group. Intake of DPA and AA may contribute to T2D development.

Effect of inulin supplementation and dietary fat source on performance, blood serum metabolites, liver lipids, abdominal fat deposition, and tissue fatty acid composition in broiler chickens

A study was conducted to evaluate the effect of adding inulin to diets containing 2 different types of fat as energy sources on performance, blood serum metabolites, liver lipids, and fatty acids of abdominal adipose tissue and breast and thigh meat. A total of 240 one-day-old female broiler chicks were randomly allocated into 1 of 6 treatments with 8 replicates per treatment and 5 chicks per pen. The experiment consisted of a 3 x 2 factorial arrangement of treatments including 3 concentrations of inulin (0, 5, and 10 g/kg of diet) and 2 types of fat [palm oil (PO) and sunflower oil (SO)] at an inclusion rate of 90 g/kg of diet. The experimental period lasted from 1 to 34 d. Dietary fat type did not affect BW gain but impaired feed conversion (P < 0.001) in birds fed the PO diets compared with birds fed the SO diets. The diets containing PO increased abdominal fat deposition and serum lipid and glucose concentrations. Triacylglycerol contents in liver were higher in the birds fed PO diets. Dietary fat type also modified fatty acids of abdominal and i.m. fat, resulting in a higher concentration of C16:0 and C18:1n-9 and a lower concentration of C18:2n-6 in the birds fed PO diets. The addition of inulin to diets modified (P = 0.017) BW gain quadratically without affecting feed conversion. Dietary inulin decreased the total lipid concentration in liver (P = 0.003) and that of triacylglycerols and very low density lipoprotein cholesterol (up to 31%) in blood serum compared with the control groups. The polyunsaturated fatty acid:saturated fatty acid ratio increased in abdominal and i.m. fat when inulin was included in the SO-containing diets. The results from the current study suggest that the addition of inulin to broiler diets has a beneficial effect on blood serum lipids by decreasing triacylglyceride concentrations The results also support the use of inulin to increase the capacity of SO for enhancing polyunsaturated fatty acid:saturated fatty acid ratio of i.m. fat in broilers.

Influence of a fat overload on lipogenic regulators in metabolic syndrome patients

Several epidemiological studies have related an increase of lipids in the postprandial state to an individual risk for the development of CVD, possibly due to the increased plasma levels of TAG and fatty acids (FA) through enzymes of FA metabolism. The interaction between nutrition and the human genome determines gene expression and metabolic response. The aim of the present study was to evaluate the influence of a fat overload on the gene mRNA levels of lipogenic regulators in peripheral blood mononuclear cells (PBMC) from patients with the metabolic syndrome. The study included twenty-one patients with criteria for the metabolic syndrome who underwent a fat overload. Measurements were made before and after the fat overload of anthropometric and biochemical variables and also the gene mRNA levels of lipogenic factors. The main results were that the fat overload led to an increased mRNA levels of sterol regulatory element binding protein-1 (SREBP1), retinoid X receptor α (RXRα) and liver X receptor α (LXRα) in PBMC, and this increase was associated with the FA synthase (FASN) mRNA levels. We also found that TAG levels correlated with FASN mRNA levels. In addition, there was a positive correlation of SREBP1 with RXRα and of LXRα with the plasma lipoperoxide concentration. The fat overload led to an increase in regulators of lipogenesis in PBMC from patients with the metabolic syndrome.

The caliciviruses

The caliciviruses are by far the major cause of non-bacterial gastroenteritis, highly infectious, and have a rapid and severe onset of symptoms. Studies on this family of viruses have been hampered by the lack of animal model and tissue culture system. However, recent advances in protein expression systems and the development of a mouse norovirus animal model has led to rapid advances in our understanding of these viruses with regard to structure and the host immune response. Our current understanding of this important family of viruses is reviewed here.

In vivoregulation of rainbow trout lipolysis by catecholamines

Lipolysis provides fatty acids that support key life processes by functioning as membrane components, oxidative fuels and metabolic signals. It is commonly measured as the rate of appearance of glycerol(Ra glycerol). Its in vivo regulation by catecholamines has been thoroughly investigated in mammals, but little information is available for ectotherms. Therefore, the goals of this study were, first, to characterize the effects of the catecholamines norepinephrine(NE) and epinephrine (Epi) on the lipolytic rate of intact rainbow trout(Oncorhynchus mykiss) and, second, to determine whether the plasma glycerol concentration is a reliable index of Ra glycerol. Our results show that baseline Ra glycerol (4.6±0.4μmol kg–1 min–1) is inhibited by NE(–56%), instead of being stimulated, as in mammals, whereas Epi has the same activating effect in both groups of vertebrates (+167%). NE-induced inhibition of fish lipolysis might play a particularly important role during aquatic hypoxia, when survival often depends on regulated metabolic depression. The plasma glycerol concentration is a poor predictor of Ra glycerol, and it should not be used as an index of lipolysis. Trout maintain a particularly high baseline lipolytic rate because only 13% of the fatty acids provided are sufficient to support total energy expenditure, whereas the remaining fatty acids must undergo reesterification(87%).

Bioinformatic profiling of the transcriptional response of adult rat cardiomyocytes to distinct fatty acids

Diabetes mellitus, obesity, and dyslipidemia increase risk for cardiovascular disease, and expose the heart to high plasma fatty acid (FA) levels. Recent studies suggest that distinct FA species are cardiotoxic (e.g., palmitate), while others are cardioprotective (e.g., oleate), although the molecular mechanisms mediating these observations are unclear. The purpose of the present study was to investigate the differential effects of distinct FA species (varying carbon length and degree of saturation) on adult rat cardiomyocyte (ARC) gene expression. ARCs were initially challenged with 0.4 mM octanoate (8:0), palmitate (16:0), stearate (18:0), oleate (18:1), or linoleate (18:2) for 24 h. Microarray analysis revealed differential regulation of gene expression by the distinct FAs; the order regarding the number of genes whose expression was influenced by a specific FA was octanoate (1,188) > stearate (740) > palmitate (590) > oleate (83) > linoleate (65). In general, cardioprotective FAs (e.g., oleate) increased expression of genes promoting FA oxidation to a greater extent than cardiotoxic FAs (e.g., palmitate), whereas the latter induced markers of endoplasmic reticulum and oxidative stress. Subsequent RT-PCR analysis revealed distinct time- and concentration-dependent effects of these FA species, in a gene-specific manner. For example, stearate- and palmitate-mediated ucp3 induction tended to be transient (i.e., initial high induction, followed by subsequent repression), whereas oleate-mediated induction was sustained. These findings may provide insight into why diets high in unsaturated FAs (e.g., oleate) are cardioprotective, whereas diets rich in saturated FAs (e.g., palmitate) are not.

Analysis of fatty acids in lung tissues using gas chromatography-mass spectrometry preceded by derivatization-solid-phase microextraction with a novel fiber

In this article, a laboratory-made sol-gel derived fiber with butyl methacrylate/hydroxy-terminated silicone oil (BMA/OH-TSO) coating was first used for headspace solid-phase microextraction (HS-SPME) of medium and long chain fatty acids after derivatization and applied to the analysis of fatty acids in lung tissues by coupling to gas chromatography-mass spectrometry (GC-MS). The experimental parameters for derivatization, HS-SPME and desorption were optimized. Fatty acids in cancerous lung tissues from five patients with lung cancer were determined under the optimized conditions. Normal lung tissues from the same five patients were used as controls. This fiber showed higher extraction efficiency for fatty acids after derivatization when compared with commercial polydimethylsiloxane (PDMS) and polydimethylsiloxane-divinylbenzene (PDMS/DVB) fibers due to the three-dimensional network in the coating. The method presented in this paper showed satisfactory precision, accuracy, linearity and limits of detection (LODs). The relative standard deviation values were below 13.3% (n=5) and the recoveries obtained ranged from 76.35% to 107.0%. The results obtained using the SPME method were also compared with those got by using liquid-liquid extraction (LLE) technique. It was found that the sensitivity could be enhanced by the SPME method. The analysis of the cancerous lung tissues and normal controls from five patients with lung cancer indicated that the main components of lung tissue were palmitic acid (C16:0), stearic acid (C18:0) and lignoceric acid (C24:0). A comparison between the levels of the fatty acids in cancerous lung tissues and normal controls from the same a patient with lung cancer shows that most of the saturated fatty acids showed higher levels in cancerous lung tissues, while unsaturated fatty acids showed higher levels in normal controls on the whole.

Effects of dietary fatty acids on insulin sensitivity and secretion

Globalization and global market have contributed to increased consumption of high-fat, energy-dense diets, particularly rich in saturated fatty acids( SFAs). Polyunsaturated fatty acids (PUFAs) regulate fuel partitioning within the cells by inducing their own oxidation through the reduction of lipogenic gene expression and the enhancement of the expression of those genes controlling lipid oxidation and thermogenesis. Moreover, PUFAs prevent insulin resistance by increasing membrane fluidity and GLUT4 transport. In contrast, SFAs are stored in non-adipocyte cells as triglycerides (TG) leading to cellular damage as a sequence of their lipotoxicity. Triglyceride accumulation in skeletal muscle cells (IMTG) derives from increased FA uptake coupled with deficient FA oxidation. High levels of circulating FAs enhance the expression of FA translocase the FA transport proteins within the myocites. The biochemical mechanisms responsible for lower fatty acid oxidation involve reduced carnitine palmitoyl transferase (CPT) activity, as a likely consequence of increased intracellular concentrations of malonyl-CoA; reduced glycogen synthase activity; and impairment of insulin signalling and glucose transport. The depletion of IMTG depots is strictly associated with an improvement of insulin sensitivity, via a reduced acetyl-CoA carboxylase (ACC) mRNA expression and an increased GLUT4 expression and pyruvate dehydrogenase (PDH) activity. In pancreatic islets, TG accumulation causes impairment of insulin secretion. In rat models, beta-cell dysfunction is related to increased triacylglycerol content in islets, increased production of nitric oxide, ceramide synthesis and beta-cell apoptosis. The decreased insulin gene promoter activity and binding of the pancreas-duodenum homeobox-1 (PDX-1) transcription factor to the insulin gene seem to mediate TG effect in islets. In humans, acute and prolonged effects of FAs on glucose-stimulated insulin secretion have been widely investigated as well as the effect of high-fat diets on insulin sensitivity and secretion and on the development of type 2 diabetes.

Control of gene expression by fatty acids

The last decade provided evidence that major (glucose, fatty acids, amino acids) or minor (iron, vitamin, etc.) dietary constituents regulated gene expression in an hormonal-independent manner. This review focuses on molecular mechanisms by which fatty acids control the expression genes encoding regulatory protein involved in their own metabolism. Nonesterified fatty acids or their CoA derivatives seem to be the main signals involved in the transcriptional effect of long-chain fatty acids. The effects of fatty acids are mediated either directly owing to their specific binding to various nuclear receptors (PPAR, LXR, HNF-4alpha) leading to changes in the trans-activating activity of these transcription factors, or indirectly as the result of changes in the abundance of regulatory transcription factors (SREBP-1c, ChREBP, etc.). The relative contribution of each transcription factor in fatty acid-induced positive or negative gene expression is discussed.

Regioselective cis-trans isomerization of arachidonic double bonds by thiyl radicals: the influence of phospholipid supramolecular organization

Trans unsaturated fatty acids in humans may be originated by two different contributions. The exogenous track is due to dietary supplementation of trans fats and the endogenous path deals with free-radical-catalyzed cis-trans isomerization of fatty acids. Arachidonic acid residue (5c,8c,11c,14c-20:4), which has only two out of the four double bonds deriving from the diet, was used to differentiate the two paths and to assess the importance of a radical reaction. A detailed study on the formation of trans phospholipids catalyzed by the HOCH2CH2S* radical was carried out on L-alpha-phosphatidylcholine from egg lecithin and 1-stearoyl-2-arachidonoyl-L-alpha-phosphatidylcholine (SAPC) in homogeneous solution or in large unilamellar vesicles (LUVET). Thiyl radicals were generated from the corresponding thiol by either gamma-irradiation or UV photolysis, and the reaction course was followed by GC, Ag/TLC, and 13C NMR analyses. The isomerization was found to be independent of cis double bond location (random process) in i-PrOH solution. In the case of vesicles, the supramolecular organization of lipids produced a dramatic change of the isomerization outcome: (i) in egg lecithin, the reactivity of arachidonate moieties is higher than that of oleate and linoleate residues, (ii) in the linoleate residues of egg lecithin, the 9t,12c-18:2 isomer prevailed on the 9c,12t-18:2 isomer (3:1 ratio), and (iii) a regioselective isomerization of SAPC arachidonate residues occurred in the 5 and 8 positions. This effect of "positional preference" indicates that thiyl radicals entering the hydrophobic region of the membrane bilayer start to isomerize polyunsaturated fatty acid residues having the double bonds nearest to the membrane surfaces. We propose that arachidonic acid and its trans isomers can function as biomarkers in membranes for distinguishing the two trans fatty acid-forming pathways.

Cloning and nutritional regulation of a Delta6-desaturase-like enzyme in the marine teleost gilthead seabream (Sparus aurata)

Marine fish are presumed to have a lower capacity than freshwater fish for the bioconvertion of 18C fatty acids into 20-22C highly unsaturated fatty acids (HUFA). The present work investigated the first step of this pathway, the Delta6-desaturation, in gilthead seabream. A full-length desaturase-like cDNA was identified from total RNA extracted from viscera of juvenile fish fed for 96 days on an experimental HUFA-free diet containing olive oil as the sole lipid source. The open reading frame encodes a 445-amino acid peptide that contains two membrane-spanning domains, three histidine-rich regions, and a cytochrome b(5) domain, which are characteristic of Delta6- and Delta5-desaturases. Predicted protein sequence of seabream desaturase-like indicated a high percentage of identity with mammalian Delta6-desaturases (approx. 65%). Northern analysis showed two transcripts of approximately 3.7 and 1.8 kb which were highly expressed in fish fed on HUFA-free diet and slightly expressed in fish fed on HUFA-rich diet. The fatty acid profile of the former group was characterized by high levels of Delta6-desaturation products (18:2 n-9 and 20:2 n-9) with no detectable levels of Delta5-desaturation product (20:3n-9). These results demonstrate for the first time the presence and nutritional modulation of a Delta6-desaturase-like cDNA in a marine fish.

Recent advances in molecular cloning of fatty acid desaturase genes and the regulation of their expression by dietary vitamin A and retinoic acid

Vitamin A, as an essential micronutrient, is involved in higher animals in embryonic development and postnatal growth, reproduction and maintenance of normal skin, immunity and vision. Recently, studies in vivo and in cell lines have shown that vitamin A and its active metabolite, retinoic acid, regulate the expression of fatty acid desaturases including stearoyl-CoA desaturase and delta-5 desaturase. Whereas the former desaturase catalyzes the formation of monounsaturated from saturated fatty acids, the latter enzyme is involved in the desaturation pathway of dietary essential fatty acids for production of polyunsaturated fatty acids. The reaction products of these desaturases serve as critical regulators in a wide range of physiological processes which include fetal growth and development, reproduction, cell differentiation, immune and inflammatory responses.

The E-box like sterol regulatory element mediates the suppression of human Delta-6 desaturase gene by highly unsaturated fatty acids

Delta-6 Desaturase (D6D) catalyzes the first step of the synthesis of highly unsaturated fatty acids (HUFA) that play pivotal roles in many biological functions. The D6D expression is under feedback regulation by dietary HUFA. We co-transfected D6D promoter-reporter constructs to HepG2 cells with an expression vector of nuclear form sterol regulatory element binding protein-1c (SREBP-1c). A 90-bp region of the D6D promoter was required for the activation by SREBP-1c as well as for the suppression of the promoter activity by HUFA. The region contained two candidates of sterol regulatory element (SRE). Mutation analysis identified E-box like SRE (SRE-2) as essential for both SREBP-1c activation and HUFA suppression. SRE-2 has a core sequence of CAGCAG, and is also conserved in stearoyl CoA desatruases. Because HUFA are primarily incorporated into phospholipids (PL), our results suggest that the primary role of SREBP-1c in liver is the regulation of fatty acid supply for PL rather than for triglycerides.

Effects of dietary fat types on body fatness, leptin, and ARC leptin receptor, NPY, and AgRP mRNA expression

Some, but not all, fats are obesogenic. The aim of the present studies was to investigate the effects of changing type and amount of dietary fats on energy balance, fat deposition, leptin, and leptin-related neural peptides: leptin receptor, neuropeptide Y (NPY), agouti-related peptide (AgRP), and proopiomelanocortin (POMC), in C57Bl/6J mice. One week of feeding with a highly saturated fat diet resulted in ~50 and 20% reduction in hypothalamic arcuate NPY and AgRP mRNA levels, respectively, compared with a low-fat or an n-3 or n-6 polyunsaturated high-fat (PUFA) diet without change in energy intake, fat mass, plasma leptin levels, and leptin receptor or POMC mRNA. Similar neuropeptide results were seen at 7 wk, but by then epididymal fat mass and plasma leptin levels were significantly elevated in the saturated fat group compared with low-fat controls. In contrast, fat and leptin levels were reduced in the n-3 PUFA group compared with all other groups. At 7 wk, changing the saturated fat group to n-3 PUFA for 4 wk completely reversed the hyperleptinemia and increased adiposity and neuropeptide changes induced by saturated fat. Changing to a low-fat diet was much less effective. In summary, a highly saturated fat diet induces obesity without hyperphagia. A regulatory reduction in NPY and AgRP mRNA levels is unable to effectively counteract this obesogenic drive. Equally high fat diets emphasizing PUFAs may even protect against obesity.

Mitochondrial proteins in hypertrophy and atrophy: a transcript analysis in rat heart

1. Metabolic processes are acutely and chronically regulated in response to changes in the workload of the heart. Acute changes in cardiac work result in activation and inactivation of existing enzymes and in altered fluxes through existing metabolic pathways. Sustained or chronic changes in cardiac work result in both trophic and transcriptional alterations. 2. The metabolic consequences of a sustained increase or decrease in the workload of the heart are surprisingly uniform and consist of a switch from the predominant oxidation of fatty acids to oxidation of glucose. 3. This switch is reflected in the changes of the transcript levels of three key regulators of mitochondrial function: pyruvate dehydrogenase kinase 4 (PDK4), which phosphorylates and inactivates the pyruvate dehydrogenase complex, malonyl-CoA decarboxylase (MCD), which regulates malonyl-CoA levels and, therefore, rates of beta-oxidation of long-chain fatty acids, and uncoupling protein 3 (UCP-3), which uncouples the oxidative phosphorylation of ADP. 4. The transcript levels of all three proteins are downregulated in hypertrophy as well as in atrophy of rat heart. All three transcripts are transcriptionally regulated by the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha). 5. Diminished expression of PPARalpha and PPARalpha-regulated genes constitutes an adaptive mechanism in response to altered workload, because reactivation of PPARalpha in hypertrophied heart results in severe contractile dysfunction.

A unique defect in the regulation of visceral fat cell lipolysis in the polycystic ovary syndrome as an early link to insulin resistance

The etiology of polycystic ovary syndrome (PCOS) is unknown. However, PCOS has a strong resemblance to the insulin resistance (metabolic) syndrome, where an increased rate of visceral fat cell lipolysis is believed to play a pathophysiological role. We hypothesized that primary defects in visceral lipolysis might also exist in PCOS. Ten young, nonobese, and otherwise healthy PCOS women were compared with 13 matched control women. In vitro lipolysis regulation and stoichiometric properties of the final step in lipolysis activation, namely the protein kinase A (PKA)-hormone sensitive lipase (HSL) complex, were investigated in isolated visceral (i.e., omental) fat cells. Body fat distribution and circulating levels of insulin, glucose, and lipids were normal in PCOS women. However, in vivo insulin sensitivity was slightly decreased (P = 0.03). Catecholamine-induced adipocyte lipolysis was markedly (i.e., about twofold) increased in PCOS women due to changes at the postreceptor level, although there was no change in the antilipolytic properties of visceral fat cells. Western blot analyses of visceral adipose tissue showed twofold increased levels of the catalytic and the regulatory Ialpha components of PKA. In contrast, the regulatory RIIbeta component of PKA was almost 50% decreased in visceral adipose tissue in PCOS women. Recent studies on genetically modified mice have shown that a similar transition in the regulatory PKA units induces an increased lipolytic response to catecholamines. Further analysis showed that the level of HSL-short, an enzymatically inactive splice form of HSL, was decreased in PCOS (P < 0.01). The altered lipolysis in PCOS is different from that observed in visceral fat cells in the insulin resistance syndrome that occurs at the level of adrenergic receptors. We concluded that increased catecholamine-induced lipolysis in visceral fat cells may be due to unique alterations in the stoichiometric properties of the adipose PKA-HSL holoenzymes. This could be an early and possibly primary lipolysis defect in PCOS.

The clinicopathologic spectrum and management of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFD) comprises a spectrum of conditions characterized by the presence of predominantly macrovesicular fatty change in the liver and the absence of alcohol consumption in amounts considered detrimental to the liver. The histologic spectrum of NAFLD includes fatty liver alone or steatohepatitis (NASH). Nonalcoholic steatohepatitis is associated with increasing fibrosis is some cases and may progress to cirrhosis. Nonalcoholic fatty liver disease is often associated with insulin resistance. It is likely that there are one or more additional pathophysiologic defects in those with NASH, rendering them more susceptible to injury from oxidative stress. The clinical and histologic features of NASH are described, and an approach to the diagnosis and treatment of NAFLD is provided.

Adaptive increase in pyruvate dehydrogenase kinase 4 during starvation is mediated by peroxisome proliferator-activated receptor alpha

Pyruvate dehydrogenase kinase isoform 4 (PDK4) is upregulated by starvation in many tissues of the body during starvation. This causes inactivation of the pyruvate dehydrogenase complex which blocks pyruvate oxidation and conserves lactate and alanine for gluconeogenesis. Enhanced PDK4 expression may be caused by the increase in free fatty acids that occurs during starvation. Free fatty acids can activate peroxisome proliferator-activated receptor alpha (PPARalpha), and activation of PPARalpha can promote PDK4 expression. This model is supported by the findings reported here that WY-14,643, a synthetic PPARalpha activator, increases PDK4 expression in wild-type mice but not in PPARalpha-null mice. Starvation likewise increases the expression of PDK4 in tissues of wild-type mice but not in tissues of PPARalpha-null mice. These findings document the functional importance of PPARalpha for PDK4 expression during starvation and suggest an important role for elevated free fatty acids in the induction.

Regulation of cardiac and skeletal muscle malonyl-CoA decarboxylase by fatty acids

Malonyl-CoA decarboxylase (MCD) catalyzes the degradation of malonyl-CoA, an important modulator of fatty acid oxidation. We hypothesized that increased fatty acid availability would increase the expression and activity of heart and skeletal muscle MCD, thereby promoting fatty acid utilization. The results show that high-fat feeding, fasting, and streptozotocin-induced diabetes all significantly increased the plasma concentration of nonesterified fatty acids, with a concomitant increase in both rat heart and skeletal muscle MCD mRNA. Upon refeeding of fasted animals, MCD expression returned to basal levels. Fatty acids are known to activate peroxisome proliferator-activated receptor-alpha (PPARalpha). Specific PPARalpha stimulation, through Wy-14643 treatment, significantly increased the expression of MCD in heart and skeletal muscle. Troglitazone, a specific PPARgamma agonist, decreased MCD expression. The sensitivity of MCD induction by fatty acids and Wy-14643 was soleus > extensor digitorum longus > heart. High plasma fatty acids consistently increased MCD activity only in solei, whereas MCD activity in the heart actually decreased with high-fat feeding. Pressure overload-induced cardiac hypertrophy, in which PPARalpha expression is decreased (and fatty acid oxidation is decreased), resulted in decreased MCD mRNA and activity, an effect that was dependent on fatty acids. The results suggest that fatty acids induce the expression of MCD in rat heart and skeletal muscle. Additional posttranscriptional mechanisms regulating MCD activity appear to exist.

Long-chain fatty acids regulate liver carnitine palmitoyltransferase I gene (L-CPT I) expression through a peroxisome-proliferator-activated receptor alpha (PPARalpha)-independent pathway

Liver carnitine palmitoyltransferase I (L-CPT I) catalyses the transfer of long-chain fatty acid (LCFA) for translocation across the mitochondrial membrane. Expression of the L-CPT I gene is induced by LCFAs as well as by lipid-lowering compounds such as clofibrate. Previous studies have suggested that the peroxisome-proliferator-activated receptor alpha (PPARalpha) is a common mediator of the transcriptional effects of LCFA and clofibrate. We found that free LCFAs rather than acyl-CoA esters are the signal metabolites responsible for the stimulation of L-CPT I gene expression. Using primary culture of hepatocytes we found that LCFAs failed to stimulate L-CPT I gene expression both in wild-type and PPARalpha-null mice. These results suggest that the PPARalpha-knockout mouse does not represent a suitable model for the regulation of L-CPT I gene expression by LCFAs in the liver. Finally, we determined that clofibrate stimulates L-CPT I through a classical direct repeat 1 (DR1) motif in the promoter of the L-CPT I gene while LCFAs induce L-CPT I via elements in the first intron of the gene. Our results demonstrate that LCFAs can regulate gene expression through PPARalpha-independent pathways and suggest that the regulation of gene expression by dietary lipids is more complex than previously proposed.

Keloids in rural black South Africans. Part 1: general overview and essential fatty acid hypotheses for keloid formation and prevention

In the first part of this study a general overview on the hypertrophic scar and keloid phenomena regarding history, epidemiology, histopathology and aetiology, in general, together with an essential fatty acid approach as basis for hypotheses of keloid formation and prevention are given. Upon reviewing the literature in planning a strategy for prevention and treatment of keloids, one encounters an overwhelming amount of hypotheses on this topic. Based on a preliminary study on total fatty acid compositions in keloids, compared with normal skin of keloid prone and non-keloid prone patients, there can be argued as follows: an essential fatty acid deficiency of precursors and inflammatory competitors for arachidonic acid may be a factor in the multifactorial aetiology of keloid formations, and apart from a local essential fatty acid deficiency in the wound area, nutrition may also be a contributing factor in rural black South Africans. To confirm or refute the stated hypotheses of the role of essential fatty acids in keloid formation and prevention (outlined in this part of the study), dietary questionnaires and blood (plasma and red blood cell) phospholipid analyses for general information and true fatty acid intake and metabolism, respectively, in the diets of these patients (outlined in part II of this study), as well as a lipid model for keloid formations regarding phospholipids, triglycerides, cholesterol esters and free fatty acids (outlined in part III of this study), are given. The purpose of this comprehensive fatty acid study was an attempt to assess the enigma surrounding keloids and to end the nightmare of the plastic and reconstructive surgeon, since these dermal tumours are notoriously recurrent.

Insulin resistance with aging: effects of diet and exercise

Insulin resistance, a reduction in the rate of glucose disposal elicited by a given insulin concentration, is present in individuals who are obese, and those with diabetes mellitus, and may develop with aging. Methods which are utilised to measure insulin sensitivity include the hyperinsulinaemic-euglycaemic and hyperglycaemic clamps and the intravenous glucose tolerance tests. Several hormones and regulatory factors affect insulin action and may contribute to the insulin resistance observed in obesity. In addition, abnormal free fatty acid metabolism plays an important role in insulin resistance and the abnormal carbohydrate metabolism seen in individuals who are obese or diabetic. Thus, the mechanisms underlying the development of insulin resistance are multifactorial, and also involve alterations of the insulin signalling pathway. Aging is associated with an increase in bodyweight and fat mass. Not only is abdominal fat associated with hyperinsulinaemia but visceral adiposity is correlated with insulin resistance as well. Modifications of the changes in body composition with aging by diet and exercise training could delay the onset of insulin resistance. Weight loss and aerobic and resistive exercise training result in losses of total body fat and abdominal fat. Several studies report that bodyweight loss increases insulin sensitivity and improves glucose tolerance. In addition, the insulin resistance observed in aged persons can be modified by physical training. Longitudinal studies indicate significant improvements in glucose metabolism with aerobic exercise training in middle-aged and older men and women. Moreover, the improvements in insulin sensitivity with resistive training are similar in magnitude to those achieved with aerobic exercise. The improvements in glucose metabolism after bodyweight loss and exercise training may in some cases be partially attributed to changes in body composition, including reductions in total and central body fat. Yet, additional changes in skeletal muscle, blood flow and other mechanisms likely interact to modify insulin resistance with exercise training. Lifestyle modifications including bodyweight loss and physical activity provide health benefits and functional gains and should be promoted to increase insulin sensitivity and prevent glucose intolerance and type 2 diabetes mellitus in older adults.

cDNA cloning, genomic structure, and chromosomal localization of three members of the human fatty acid desaturase family

The insertion of double bonds into specific positions of fatty acids is achieved by the action of distinct desaturase enzymes. Here we report the cloning and characterization of three members of the fatty acid desaturase (FADS) gene family in humans. Initially identified as cDNA fragments by direct cDNA selection within a defined 1.4-Mb region in 11q12-q13.1, full-length fatty acid desaturase-1 (FADS1) and fatty acid desaturase-2 (FADS2) transcripts were obtained by EST sequence assembly. A third member, fatty acid desaturase-3 (FADS3), was identified in silico revealing 62 and 70% nucleotide sequence identity with FADS1 and FADS2, respectively. The three genes are clustered within 92 kb of genomic DNA located 2 kb telomeric to FEN1 and 50 kb centromeric to VMD2 and are likely to have arisen evolutionarily from gene duplication as they share a remarkably similar exon/intron organization. Protein database searches identified FADS1, FADS2, and FADS3 as fusion products composed of an N-terminal cytochrome b5-like domain and a C-terminal multiple membrane-spanning desaturase portion.

Polyunsaturated fatty acid regulation of gene transcription: a mechanism to improve energy balance and insulin resistance

This review addresses the hypothesis that polyunsaturated fatty acids (PUFA), particularly those of the n-3 family, play essential roles in the maintenance of energy balance and glucose metabolism. The data discussed indicate that dietary PUFA function as fuel partitioners in that they direct glucose toward glycogen storage, and direct fatty acids away from triglyceride synthesis and assimilation and toward fatty acid oxidation. In addition, the n-3 family of PUFA appear to have the unique ability to enhance thermogenesis and thereby reduce the efficiency of body fat deposition. PUFA exert their effects on lipid metabolism and thermogenesis by upregulating the transcription of the mitochondrial uncoupling protein-3, and inducing genes encoding proteins involved in fatty acid oxidation (e.g. carnitine palmitoyltransferase and acyl-CoA oxidase) while simultaneously down-regulating the transcription of genes encoding proteins involved in lipid synthesis (e.g. fatty acid synthase). The potential transcriptional mechanism and the transcription factors affected by PUFA are discussed. Moreover, the data are interpreted in the context of the role that PUFA may play as dietary factors in the development of obesity and insulin resistance. Collectively the results of these studies suggest that the metabolic functions governed by PUFA should be considered as part of the criteria utilized in defining the dietary needs for n-6 and n-3 PUFA, and in establishing the optimum dietary ratio for n-6:n-3 fatty acids.

Diet composition and insulin action in animal models

Critical insights into the etiology of insulin resistance have been gained by the use of animal models where insulin action has been modulated by strictly controlled dietary interventions not possible in human studies. Overall, the literature has moved from a focus on macronutrient proportions to understanding the unique effects of individual subtypes of fats, carbohydrates and proteins. Substantial evidence has now accumulated for a major role of dietary fat subtypes in insulin action. Intake of saturated fats is strongly linked to development of obesity and insulin resistance, while that of polyunsaturated fats (PUFAs) is not. This is consistent with observations that saturated fats are poorly oxidized for energy and thus readily stored, are poorly mobilized by lipolytic stimuli, impair membrane function, and increase the expression of genes associated with adipocyte profileration (making their own home). PUFAs have contrasting effects in each instance. It is therefore not surprising that increased PUFA intake in animal models is associated with improved insulin action and reduced adiposity. Less information is available for carbohydrate subtypes. Early work clearly demonstrated that diets high in simple sugars (in particular fructose) led to insulin resistance. However, again attention has rightly shifted to the very interesting issue of subtypes of complex carbohydrates. While no differences in insulin action have yet been shown, differences in substrate flux suggest there could be long-term beneficial effects on the fat balance of diets enhanced in slowly digested/resistant starches. A new area of major interest is in protein subtypes. Recent results have shown that rats fed high-fat diets where the protein component was from casein or soy were insulin-resistant, but when the protein source was from cod they were not. These are exciting times in our growing understanding of dietary factors and insulin action. While it has been clear for some time that 'oils ain't oils', the same is now proving true for carbohydrates and proteins.

Cloning, expression, and fatty acid regulation of the human delta-5 desaturase

Arachidonic (20:4(n-6)), eicosapentaenoic (20:5(n-3)), and docosahexaenoic (22:6(n-3)) acids are major components of brain and retina phospholipids, substrates for eicosanoid production, and regulators of nuclear transcription factors. One of the two rate-limiting steps in the production of these polyenoic fatty acids is the desaturation of 20:3(n-6) and 20:4(n-3) by Delta-5 desaturase. This report describes the cloning and expression of the human Delta-5 desaturase, and it compares the structural characteristics and nutritional regulation of the Delta-5 and Delta-6 desaturases. The open reading frame of the human Delta-5 desaturase encodes a 444-amino acid peptide which is identical in size to the Delta-6 desaturase and which shares 61% identity with the human Delta-6 desaturase. The Delta-5 desaturase contains two membrane-spanning domains, three histidine-rich regions, and a cytochrome b(5) domain that all align perfectly with the same domains located in the Delta-6 desaturase. Expression of the open reading frame in Chinese hamster ovary cells instilled the ability to convert 20:3(n-6) to 20:4(n-6). Northern analysis revealed that many human tissues including skeletal muscle, lung, placenta, kidney, and pancreas expressed Delta-5 desaturase mRNA, but Delta-5 desaturase was most abundant in the liver, brain, and heart. However, in all tissues, the abundance of Delta-5 desaturase mRNA was much lower than that observed for the Delta-6 desaturase. When rats were fed a diet containing 10% safflower oil or menhaden fish oil, the level of hepatic mRNA for Delta-5 and Delta-6 desaturase was only 25% of that found in the liver of rats fed a fat-free diet or a diet containing triolein. Finally, a BLAST and Genemap search of the human genome revealed that the Delta-5 and Delta-6 desaturase genes reside in reverse orientation on chromosome 11 and that they are separated by <11,000 base pairs.

Peroxisome proliferator-activated receptors: a family of lipid-activated transcription factors

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear transcription factors that belong to the steroid receptor superfamily. This family of PPARs includes PPARalpha, PPARdelta, PPARgamma1, and PPARgamma2. These PPARs are related to the T3 and vitamin D(3) receptors and bind to a hexameric direct repeat as a heterodimeric complex with retinoid receptor Xalpha. PPARs regulate the expression of a wide array of genes that encode proteins involved in lipid metabolism, energy balance, eicosanoid signaling, cell differentiation, and tumorigenesis. A unique feature of these steroid-like receptors is that the physiologic ligands for PPARs appear to be fatty acids from the n-6 and n-3 families of fatty acids and their respective eicosanoid products. This review describes the characteristics, regulation, and gene targets for PPARs and relates their effects on gene expression to physiologic outcomes that affect lipid and glucose metabolism, thermogenesis, atherosclerosis, and cell differentiation.

Sterol regulatory element binding protein-1 expression is suppressed by dietary polyunsaturated fatty acids. A mechanism for the coordinate suppression of lipogenic genes by polyunsaturated fats

Polyunsaturated fatty acids (PUFA) coordinately suppress the transcription of a wide array of hepatic lipogenic genes including fatty acid synthase (FAS) and acetyl-CoA carboxylase. Interestingly, the over-expression of sterol regulatory element binding protein-1 (SREBP-1) induces the expression of all of the enzymes suppressed by PUFA. This observation led us to hypothesize that PUFA coordinately inhibit lipogenic gene transcription by suppressing the expression of SREBP-1. Our initial studies revealed that the SREBP-1 and FAS mRNA contents of HepG2 cells were reduced by 20:4(n-6) in a dose-dependent manner (i.e. EC(50) approximately 10 microM), whereas 18:1(n-9) had no effect. Similarly, supplementing a fat-free, high glucose diet with oils rich in (n-6) or (n-3) PUFA reduced the hepatic content of precursor and nuclear SREBP-1 60 and 85%, respectively; however, PUFA had no effect on the nuclear content of upstream stimulatory factor (USF)-1. The PUFA-dependent decrease in nuclear content of mature SREBP-1 was paralleled by a 70-90% suppression in FAS gene transcription. In contrast, dietary 18:1(n-9), i.e. triolein, had no inhibitory influence on the expression of SREBP-1 or FAS. The decrease in hepatic expression of SREBP-1 and FAS associated with PUFA ingestion was mimicked by supplementing the fat-free diet with the PPARalpha-activator, WY 14, 643. Interestingly, nuclear run-on assays revealed that changes in SREBP-1 mRNA abundance were not accompanied by changes in SREBP-1 gene transcription. These results support the concept that PUFA coordinately inhibit lipogenic gene transcription by suppressing the expression of SREBP-1 and that the PUFA regulation of SREBP-1 appears to occur at the post-transcriptional level.

Selectivity of fatty acids on lipid metabolism and gene expression

Triacylglycerols represent the main form of storage for a wide spectrum of fatty acids. Their utilization first involves mobilization from adipose tissue through lipolysis. The release of individual fatty acids from adipose tissue is selective in vitro and in vivo in animal studies and also in human subjects. Generally, fatty acids are more readily mobilized from fat cells when they are short-chain and unsaturated. This selectivity could affect the storage of individual fatty acids in adipose tissue, and their subsequent supply to tissues. The nature of the dietary fats could affect lipid homeostasis and body fat deposition. Dietary fish oil influences adipose tissue development in a site-specific manner as a function of diet and feeding period. A diet high in n-3 polyunsaturated fatty acids (PUFA) results in a preferential partitioning of ingested energy towards oxidation at the expense of storage. Fatty acids are important mediators of gene expression in the liver. Indeed, genes encoding both glycolytic and lipogenic enzymes and key metabolic enzymes involved in fatty acid oxidation are regulated by dietary PUFA. White adipose tissue could also be a target for PUFA control of gene expression. The treatment of pre-adipose cells by fatty acids induces the expression of numerous genes that encode proteins involved in fatty acid metabolism. The mechanisms of PUFA-mediated repression of gene expression in adipocytes seem to be different, at least partly, from those described in liver. Tissue-specific and site-specific factors are possibly involved in the specific effect of PUFA on gene expression, although other mechanisms cannot be excluded.

Dietary 18:3n-3 and 22:6n-3 as sources of 22:6n-3 accretion in neonatal baboon brain and associated organs

The bioequivalence of dietary linolenic acid (LNA) and docosahexaenoic acid (DHA) for brain DHA accretion was measured in neonatal baboons at 4-6 wk of age using stable isotope tracers. Neonates consumed a conventional U.S. term-infant formula devoid of long chain polyunsaturates and with an n-6/n-3 ratio of about 10:1. At 4 wk of age, neonates were dosed with either 13C LNA or 13C DHA. At 6 wk of age, neonate brain, retina, and other organs were harvested for fatty acid and isotopic analyses. The relative accretion of labeled DHA was 7-fold greater as a percentage of dose for the DHA-dosed animals compared to the LNA-dosed animals. The baboon is an omnivore that regularly consumes meat and insects; its plasma lipid profile responds similarly to humans in response to changes in feeding and living habits. These observations suggest that the baboon is a suitable model for human unsaturated fatty acid studies.

3-Thia fatty acid treatment, in contrast to eicosapentaenoic acid and starvation, induces gene expression of carnitine palmitoyltransferase-II in rat liver

The aim of the present study was to investigate the hepatic regulation and beta-oxidation of long-chain fatty acids in peroxisomes and mitochondria, after 3-thia- tetradecylthioacetic acid (C14-S-acetic acid) treatment. When palmitoyl-CoA and palmitoyl-L-carnitine were used as substrates, hepatic formation of acid-soluble products was significantly increased in C14-S-acetic acid treated rats. Administration of C14-S-acetic acid resulted in increased enzyme activity and mRNA levels of hepatic mitochondrial carnitine palmitoyltransferase (CPT)-II. CPT-II activity correlated with both palmitoyl-CoA and palmitoyl-L-carnitine oxidation in rats treated with different chain-length 3-thia fatty acids. CPT-I activity and mRNA levels were, however, marginally affected. The hepatic CPT-II activity was mainly localized in the mitochondrial fraction, whereas the CPT-I activity was enriched in the mitochondrial, peroxisomal, and microsomal fractions. In C14-S-acetic acid-treated rats, the specific activity of peroxisomal and microsomal CPT-I increased, whereas the mitochondrial activity tended to decrease. C14-S-Acetyl-CoA inhibited CPT-I activity in vitro. The sensitivity of CPT-I to malonyl-CoA was unchanged, and the hepatic malonyl-CoA concentration increased after C14-S-acetic acid treatment. The mRNA levels of acetyl-CoA carboxylase increased. In hepatocytes cultured from palmitic acid- and C14-S-acetic acid-treated rats, the CPT-I inhibitor etomoxir inhibited the formation of acid-soluble products 91 and 21%, respectively. In contrast to 3-thia fatty acid treatment, eicosapentaenoic acid treatment and starvation increased the mitochondrial CPT-I activity and reduced its malonyl-CoA sensitivity. Palmitoyl-L-carnitine oxidation and CPT-II activity were, however, unchanged after either EPA treatment or starvation. The results from this study open the possibility that the rate control of mitochondrial beta-oxidation under mitochondrion and peroxisome proliferation is distributed between an enzyme or enzymes of the pathway beyond the CPT-I site after 3-thia fatty acid treatment. It is suggested that fatty acids are partly oxidized in the peroxisomes before entering the mitochondria as acylcarnitines for further oxidation.

Fatty acids: links between genes involved in fatty acid and cholesterol metabolism

Fatty acids are a major constituent of dietary fats and form an integral part of the cellular membrane and lipoproteins. The gene regulatory potential of fatty acids has long been recognized, but the precise regulatory mechanisms are unknown. The regulatory ability of fatty acids on the expression of a number of genes together with potential mechanisms and pathways of regulation are reviewed. In this review, we emphasize a key aspect of regulation mediated by the sterol regulatory element binding-protein, and its effects on sterol regulatory elements.

Cloning, expression, and nutritional regulation of the mammalian Delta-6 desaturase

Arachidonic acid (20:4(n-6)) and docosahexaenoic acid (22:6(n-3)) have a variety of physiological functions that include being the major component of membrane phospholipid in brain and retina, substrates for eicosanoid production, and regulators of nuclear transcription factors. The rate-limiting step in the production of 20:4(n-6) and 22:6(n-3) is the desaturation of 18:2(n-6) and 18:3(n-3) by Delta-6 desaturase. In this report, we describe the cloning, characterization, and expression of a mammalian Delta-6 desaturase. The open reading frames for mouse and human Delta-6 desaturase each encode a 444-amino acid peptide, and the two peptides share an 87% amino acid homology. The amino acid sequence predicts that the peptide contains two membrane-spanning domains as well as a cytochrome b5-like domain that is characteristic of nonmammalian Delta-6 desaturases. Expression of the open reading frame in rat hepatocytes and Chinese hamster ovary cells instilled in these cells the ability to convert 18:2(n-6) and 18:3(n-3) to their respective products, 18:3(n-6) and 18:4(n-3). When mice were fed a diet containing 10% fat, hepatic enzymatic activity and mRNA abundance for hepatic Delta-6 desaturase in mice fed corn oil were 70 and 50% lower than in mice fed triolein. Finally, Northern analysis revealed that the brain contained an amount of Delta-6 desaturase mRNA that was several times greater than that found in other tissues including the liver, lung, heart, and skeletal muscle. The RNA abundance data indicate that prior conclusions regarding the low level of Delta-6 desaturase expression in nonhepatic tissues may need to be reevaluated.

Polyunsaturated fatty acids, membrane function and metabolic diseases such as diabetes and obesity

Lipids play an extraordinary range of roles in normal and deranged metabolism. In diabetes and obesity, lipids have often been seen just as impacting on the energy balance equation. New data are extending our understanding of how lipid subclasses influence carbohydrate and lipid metabolism at multiple control points: from the modulation of membrane proteins to the regulation of gene transcription.

Polyunsaturated fatty acids decrease expression of promoters with sterol regulatory elements by decreasing levels of mature sterol regulatory element-binding protein

Membrane physiology, plasma lipid levels, and intracellular sterol homeostasis are regulated by both fatty acids and cholesterol. Sterols regulate gene expression of key enzymes of cholesterol and fatty acid metabolism through proteolysis of the sterol regulatory element-binding protein (SREBP), which binds to sterol regulatory elements (SRE) contained in promoters of these genes. We investigated the effect of fatty acids on SRE-dependent gene expression and SREBP. Consistent results were obtained in three different cell lines (HepG2, Chinese hamster ovary, and CV-1) transfected with SRE-containing promoters linked to the luciferase expression vector. We show that micromolar concentrations of oleate and other polyunsaturated fatty acids (C18:2-C22:6) dose-dependently (0.075-0.6 mmol) decreased transcription of SRE-regulated genes by 20-75%. Few or no effects were seen with saturated free fatty acids. Fatty acid effects on SRE-dependent gene expression were independent and additive to those of exogenous sterols. Oleate decreased levels of the mature sterol regulatory element-binding proteins SREBP-1 and -2 and HMG-CoA synthase mRNA. Oleate had no effect in sterol regulation defective Chinese hamster ovary cells or in cells transfected with mutant SRE-containing promoters. We hypothesize that unsaturated fatty acids increase intracellular regulatory pools of cholesterol and thus affect mature SREBP levels and expression of SRE-dependent genes.

Regulation of gene expression by fatty acids

Long-chain fatty acids regulate the transcription of several genes encoding proteins involved in energetic metabolism. This review discusses the relative contribution of free fatty acids or their coenzyme A ester as metabolite signals and the possibility that the control of gene transcription could be independent of the activation of peroxisome proliferator-activated receptors.

Polyunsaturated fatty acid regulation of gene expression

For the past three decades, polyunsaturated fatty acids (PUFA) have been recognized as important energy sources and membrane components. PUFA also play key roles in many cellular events, such as gene regulation. Most recently, research has focused on identifying the mechanisms by which PUFA modulate gene transcription, mRNA stability and cellular differentiation. It is the purpose of this review to examine the effects of PUFA on gene expression in lipogenic as well as other tissues. Because the (n-3) and (n-6) series of PUFA are intimately involved in gene regulation, they will be the focus of review. The effects of other fatty acid families on gene expression are reviewed elsewhere.