Fatty acid desaturation and chain elongation in eukaryotes

TCF7l2 Regulates Fatty Acid Chain Elongase HACD3 during Lipid-Induced Stress

The transcriptional regulation of metabolic genes is crucial for maintaining metabolic homeostasis under cellular stress conditions. Transcription factor 7-like 2 (TCF7l2 or TCF4) is associated with type 2 diabetes (T2D) and functions as a transcription factor for various gluconeogenic genes. T2D often coexists with metabolic dysfunction-associated steatotic liver disease (MASLD) due to common underlying mechanisms and shared risk factors such as insulin resistance and obesity. This study demonstrates the transcriptional regulation of one of the important fatty acid chain elongases implicated in T2D, HACD3 (encoded by PTPLAD1 gene), under palmitic acid (PA)-induced stress conditions. We observed that TCF7l2 is associated with histone H3K4me3-binder protein TCF19 and is corecruited to the promoter of PTPLAD1. Upon PA treatment, the TCF19-TCF7l2 complex dissociates from the lipid chain elongase gene due to the reduced level of H3K4me3 enrichment, leading to PTPLAD1 activation. Remarkably, gene expression analysis from the PA-injected mice and NAFLD patients indicates an anticorrelation whereby reduced TCF7l2 expression enhances HACD3-mediated chain elongation and triglyceride production, thereby promoting the development of MASLD. Our findings delineate that the epigenetic mechanism of activation of lipid chain elongase genes mediated by TCF7l2 in concert with TCF19 has important implications in metabolic disorders.

Recent Insights into the Reaction Mechanisms of Non-Heme Diiron Enzymes Containing Oxoiron(IV) Complexes

Oxoiron(IV) complexes are key intermediates in the catalytic reactions of some non-heme diiron enzymes. These enzymes, across various subfamilies, activate dioxygen to generate high-valent diiron-oxo species, which, in turn, drive the activation of substrates and mediate a variety of challenging oxidative transformations. In this review, we summarize the structures, formation mechanisms, and functions of high-valent diiron-oxo intermediates in eight representative diiron enzymes (sMMO, RNR, ToMO, MIOX, PhnZ, SCD1, AlkB, and SznF) spanning five subfamilies. We also categorize and analyze the structural and mechanistic differences among these enzymes.

Role of Acyl-CoA Thioesterase 7 in Regulating Fatty Acid Metabolism and Its Contribution to the Onset and Progression of Bovine Clinical Mastitis

Clinical mastitis (CM) is a prevalent and severe inflammatory disease in dairy cows affecting the mammary glands. Fatty acid (FA) metabolism and associated enzymes are crucial for many physiological and pathological processes in dairy cows. However, the relationships among FA metabolism, FA-associated enzymes, and CM, as well as the mechanisms underlying their interactions, in dairy cows are not fully understood. The aim of this study was to characterize biological process (BP) terms, pathways, and differentially expressed proteins (DEPs) related to FA metabolism from our previous data-independent acquisition proteomic study. Six BPs involving 14 downregulated and 20 upregulated DEPs, and four pathways involving 10 downregulated and 11 upregulated DEPs related to FA synthesis and metabolism were systematically identified. Associated analysis suggested that 12 candidate DEPs obtained from BPs and pathways, especially acyl-CoA thioesterase 7 (ACOT7), regulate long-chain FA (LCFA) elongation and the biosynthesis of unsaturated FAs. Immunohistochemical and immunofluorescence staining results showed that ACOT7 was present mainly in the cytoplasm of mammary epithelial cells. The qRT-PCR and Western blotting results showed that ACOT7 mRNA and protein levels in the mammary glands of the CM group were significantly upregulated compared to those in the healthy group. This evidence indicates that ACOT7 is positively correlated with CM onset and progression in Holstein cows. These findings offer novel insights into the role of FA metabolism and related enzymes in CM and offer potential targets for the development of therapeutic strategies and biomarkers for the prevention and treatment of CM in dairy cows.

Significance of fatty acids in fish broodstock nutrition

The nutritional status of broodstock profoundly affects their reproductive performance and offspring survival. Studies on lipids and essential fatty acids in broodstock diets highlight their importance in cell structure, fecundity, fertilization, egg and larval quality, and providing metabolic energy for reproduction. Long-chain polyunsaturated fatty acids (Lc-PUFA) like DHA (22:6 n-3) and EPA (20:5 n-3) are vital for egg and larval development, while arachidonic acid (ARA) produces eicosanoids essential for reproduction. The fatty acid requirements vary by habitat; freshwater fish typically lack ∆12 and ∆15 desaturase enzymes to convert oleic acid into vital polyunsaturated fatty acids like linoleic and linolenic acids but can synthesize linoleic (18:2 n-6) and linolenic (18:3 n-3) into Lc-PUFAs such as EPA, DHA, and ARA through desaturation and elongation, whereas marine teleost cannot. Hence, broodstock feed fatty acid composition must be tailored by incorporating ingredients with a specific fatty acid composition to enhance reproductive performance. This review provides updated information on fatty acid supplementation in broodstock diets to improve reproductive outcomes in commercially important finfish, offering valuable insights for researchers, academicians, hatchery owners, and fish farmers to produce better-quality seeds.

Pathogen-Mediated Alterations of Insect Chemical Communication: From Pheromones to Behavior

Pathogens can influence the physiology and behavior of both animal and plant hosts in a manner that promotes their own transmission and dispersal. Recent research focusing on insects has revealed that these manipulations can extend to the production of pheromones, which are pivotal in chemical communication. This review provides an overview of the current state of research and available data concerning the impacts of bacterial, viral, fungal, and eukaryotic pathogens on chemical communication across different insect orders. While our understanding of the influence of pathogenic bacteria on host chemical profiles is still limited, viral infections have been shown to induce behavioral changes in the host, such as altered pheromone production, olfaction, and locomotion. Entomopathogenic fungi affect host chemical communication by manipulating cuticular hydrocarbons and pheromone production, while various eukaryotic parasites have been observed to influence insect behavior by affecting the production of pheromones and other chemical cues. The effects induced by these infections are explored in the context of the evolutionary advantages they confer to the pathogen. The molecular mechanisms governing the observed pathogen-mediated behavioral changes, as well as the dynamic and mutually influential relationships between the pathogen and its host, are still poorly understood. A deeper comprehension of these mechanisms will prove invaluable in identifying novel targets in the perspective of practical applications aimed at controlling detrimental insect species.

Flaxseed oil modulates testicular biometrics, hormone, libido, antioxidant and semen profiles in endangered Teressa goat of Andaman and Nicobar Islands

Teressa goat is a unique goat breed in Andaman and Nicobar Islands (ANI) of India. Effects of Flaxseed oil (FSO) supplementation in body weight (BW), scrotal circumference (SC), testicular volume (TV) and testicular weight (TW), endocrinological profiles, sex behavioural profiles (SBPs), oxidative stress markers and semen production and its quality profiles in rainy and dry summer season were studied in Teressa goat. Male goats (n = 12) of 3-4 years old were equally divided into control and treated groups. Treated animals received 25 mL FSO per day. Oral drenching of FSO was done in the morning before feeding the concentrate ration. Body weight, scrotal circumference, TV and TW were measured in bucks of FSO treated and untreated during rainy and dry summer seasons. Blood follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone, thyroid stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), cortisol and prolactin, total antioxidant capacity (TAC), superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and malondialdehyde (MDA) were measured in bucks of FSO treated and untreated during rainy and dry summer seasons. Libido score (LS), mating ability score (MAS) and sex behavioural score (SBS) were estimated at time of semen collection in bucks of FSO treated and untreated during rainy and dry summer seasons. Semen samples (n = 100; 50 semen samples from each season; each 25 semen samples from control and treatment groups per season) were collected and analysed for semen quality profiles. One-way ANOVA (control rainy, control dry, treated rainy and treated dry) revealed that BW, SC, TV and TW, FSH, LH, testosterone, TSH, T3 and T4 were higher (P < 0.05) and cortisol and prolactin were lower (P < 0.05) in FSO treated bucks of rainy season followed by untreated bucks of rainy season, FSO treated bucks of dry summer season and were lower (P < 0.05) in untreated bucks of dry summer season. Similarly, TAC, CAT, SOD and GSH, LS, MAS and SBS, and volume, pH, sperm concentration, mass activity, total motility (TM), viability, acrosomal integrity (AcI), plasma membrane integrity (PMI) and nuclear integrity (NI) were higher (P < 0.05) and MDA and TSA were lower (P < 0.05) in FSO treated bucks of rainy season followed by FSO treated bucks of dry summer season, untreated bucks of rainy season and were lower (P < 0.05) in untreated bucks of dry summer season. The results of the present study indicated that the breeding bucks suffered physiological stress (higher cortisol), oxidative stress (higher MDA and deficiency of antioxidants), hormonal imbalance (higher prolactin and cortisol and deficiency of gonadotropins, gonadal hormone and thyroid hormones) and infertility due to poor libido and poor semen production and its quality profiles during dry summer season. Thus, dry summer was more stressful season compared to rainy season for the goat bucks. FSO supplementation mitigated these stresses and improved the scrotal and testicular biometrics, libido, antioxidants, hormones and semen quality profiles in Teressa goat bucks. The current study concluded that FSO effectively improved the hormones, libido, antioxidant profiles, and scrotal and testicular biometrics with cascading beneficial effects on semen quality profiles in Teressa goat bucks under humid tropical island ecosystem of Andaman and Nicobar Islands.

Freshwater Macrophytes: A Potential Source of Minerals and Fatty Acids for Fish, Poultry, and Livestock

The freshwater macrophytes are abundant in tropical and subtropical climates. These macrophytes may be used as feed ingredients for fish and other animals. The nutritional value of twelve freshwater-cultured macrophytes was evaluated in the present study. Significantly higher crude protein (36.94–36.65%) and lipid (8.13–7.62%) were found in Lemna minor and Spirodela polyrhiza; ash content was significantly higher in Hydrilla verticillata, Wolffia globosa, and Pistia stratiotes (20.69–21.00%) compared with others. The highest levels of sodium, magnesium, chromium, and iron levels were recorded in P. stratiotes. H. verticillata was a rich source of copper, manganese, cobalt, and zinc; the contents of calcium, magnesium, strontium, and nickel were highest in S. polyrhiza. Selenium and potassium contents were higher in Salvinia natans and W. globosa, respectively. The n-6 and n-3 polyunsaturated fatty acids (PUFAs) contents were significantly higher in W. globosa and Ipomoea aquatica, respectively compared with others. Linoleic and α-linolenic acids were dominant n-6 and n-3 PUFAs. The highest value (4.04) of n-3/n-6 was found in I. aquatica. The ratio ranged from 0.61 to 2.46 in other macrophytes. This study reveals that macrophytes are rich sources of minerals, n-6 and n-3 PUFAs.

Endogenous LC-PUFA biosynthesis capability in commercially important mollusks

Mollusks are excellent dietary sources for LC-PUFA. However, the main challenge limiting mollusk production is the high mortality rate of molluskan larvae in early life cycle stages. This paper reviews scientific evidences on molecular and biochemical studies of LC-PUFA biosynthesis in commercially important molluskan species. It carefully summarizes the pertinent data published on specific research questions to improve the understanding of the diverse evidences. It is helpful to clarify the current state of research and determine topics for future studies on LC-PUFA biosynthesis in mollusks. From the analysis of published data, mollusks have the ability to biosynthesis LC-PUFA to a certain extent. LC-PUFA biosynthesis information of commercially important molluskan species can be useful to determine the fatty acids essential for their diet. Therefore, specific management strategies or feeds can be developed to strengthen the industry by improving the health and survival rate of molluskan larvae.

Inter- and intraspecific differences in rotifer fatty acid composition during acclimation to low-quality food

Biochemical food quality constraints affect the performance of consumers and mediate trait variation among and within consumer species. To assess inter- and intraspecific differences in fatty acid retention and conversion in freshwater rotifers, we provided four strains of two closely related rotifer species, Brachionus calyciflorus sensu stricto and Brachionus fernandoi, with food algae differing in their fatty acid composition. The rotifers grazed for 5 days on either Nannochloropsis limnetica or Monoraphidium minutum, two food algae with distinct polyunsaturated fatty acid (PUFA) profiles, before the diets were switched to PUFA-free Synechococcus elongatus, which was provided for three more days. We found between- and within-species differences in rotifer fatty acid compositions on the respective food sources and, in particular, highly specific acclimation reactions to the PUFA-free diet. The different reactions indicate inter- but also intraspecific differences in physiological traits, such as PUFA retention, allocation and bioconversion capacities, within the genus Brachionus that are most likely accompanied by differences in their nutritional demands. Our data suggest that biochemical food quality constraints act differently on traits of closely related species and of strains of a particular species and thus might be involved in shaping ecological interactions and evolutionary processes. This article is part of the theme issue 'The next horizons for lipids as 'trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

The Various Roles of Fatty Acids

Lipids comprise a large group of chemically heterogeneous compounds. The majority have fatty acids (FA) as part of their structure, making these compounds suitable tools to examine processes raging from cellular to macroscopic levels of organization. Among the multiple roles of FA, they have structural functions as constituents of phospholipids which are the "building blocks" of cell membranes; as part of neutral lipids FA serve as storage materials in cells; and FA derivatives are involved in cell signalling. Studies on FA and their metabolism are important in numerous research fields, including biology, bacteriology, ecology, human nutrition and health. Specific FA and their ratios in cellular membranes may be used as biomarkers to enable the identification of organisms, to study adaptation of bacterial cells to toxic compounds and environmental conditions and to disclose food web connections. In this review, we discuss the various roles of FA in prokaryotes and eukaryotes and highlight the application of FA analysis to elucidate ecological mechanisms. We briefly describe FA synthesis; analyse the role of FA as modulators of cell membrane properties and FA ability to store and supply energy to cells; and inspect the role of polyunsaturated FA (PUFA) and the suitability of using FA as biomarkers of organisms.

Biosynthesis of Polyunsaturated Fatty Acids in the Razor Clam Sinonovacula constricta: Characterization of Δ5 and Δ6 Fatty Acid Desaturases

To investigate the endogenous long-chain polyunsaturated fatty acid (LC-PUFA) biosynthetic ability in Sinonovacula constricta, fatty acid desaturases (Fads) of this bivalve, namely, Scfad5a, Scfad5b, and Scfad6, were cloned and characterized in the current study. Meanwhile, the tissue distributions of S. constricta Fads and fatty acids (FAs) were examined. Heterologous expression in yeasts confirmed that Scfad5a and Scfad5b were both Δ5 Fads, while Scfad6 was a Δ6 Fad. However, compared with Fads in other organisms, the desaturation activities of S. constricta Fads were relatively low (especially for Scfad6), indicating an adaptation to living conditions. S. constricta Fads were expressed in all tissues examined, and particularly high expressions were found in intestine and gonad. Moreover, FAs were differently distributed among tissues, which might be correlated with their corresponding physiological roles. Taken together, the results provided an insight into LC-PUFA biosynthesis in S. constricta. Notably, Scfad6 was the first functionally characterized Δ6 Fad in marine molluscs to date.

Dietary n-3 PUFAs improve fresh and post-thaw semen quality in Holstein bulls via alteration of sperm fatty acid composition

The goal of this study was to investigate the effect of fish oil-supplemented diet on fresh and post-thaw semen quality and sperm lipid composition in bulls. Bulls were randomly assigned to two groups (n = 6). Six bulls were used as the control group and six received the fish oil (1.2% dry matter of total diet) for 11 weeks. Semen was individually collected from each bull and frozen biweekly. Semen volume, sperm concentration, viability, progressive motility, and fatty acid profile of sperm were measured in 1st, 3rd, 5th, 7th, 9th, and 11th week of experiment. Viability, progressive motility, and fatty acid profile of post-thaw sperm were also measured in 3rd, 5th, 9th, and 11th week of experiment. Data were analyzed with using Proc GLM or MIXED (for repeated measurement data) in SAS program. The fish oil-supplemented diet increased the semen volume and sperm concentration. The fish oil-supplemented diet also altered the viability, progressive motility, and fatty acid profile of fresh and post-thaw sperm. In conclusion, feeding a fish oil-enriched diet via alteration of fatty acid profile of sperm lipid could improve in vitro quality of fresh and post-thaw sperm in Holstein bulls.

Feeding laying hens stearidonic acid-enriched soybean oil, as compared to flaxseed oil, more efficiently enriches eggs with very long-chain n-3 polyunsaturated fatty acids

The desaturation of α-linolenic acid (ALA) to stearidonic acid (SDA) is considered to be rate-limiting for the hepatic conversion of ALA to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in humans, rodents, and chickens. Thus, we hypothesized that feeding laying hens SDA, as a component of the oil derived from the genetic modification of the soybean, would bypass this inefficient metabolic step and result in the enrichment of eggs with EPA and DHA at amounts comparable to that achieved by direct supplementation of hens' diet with these very long-chain (VLC) n-3 polyunsaturated fatty acids (PUFAs). In a 28-d study, laying hens incorporated 0.132 mg, 0.041 mg, or 0.075 mg of VLC n-3 PUFAs into egg yolk for each milligram of ingested dietary ALA derived primarily from conventional soybean oil (CON), dietary ALA derived primarily from flaxseed oil (FLAX), or dietary SDA derived from SDA-enriched soybean oil, respectively. Moreover, the amounts of total yolk VLC n-3 PUFAs in eggs from hens fed the CON (51 mg), FLAX (91 mg), or SDA (125 mg) oils were markedly less than the 305 mg found in eggs from fish oil-fed hens. Unexpectedly, SDA appeared to be more readily incorporated into adipose tissue than into egg yolk. Since egg yolk FAs typically reflect the hens' dietary pattern, these tissue-specific differences suggest the existence of an alternate pathway for the hepatic secretion and transport of SDA in the laying hen.

Increasing intake of essential fatty acids from milk replacer benefits performance, immune responses, and health of preweaned Holstein calves

The objective was to evaluate the effect of feeding increasing amounts of essential fatty acids (FA) in milk replacer (MR) during the first 60 d of life on growth, health, and immunity of Holstein calves. Calves were born from dams fed low concentrations of total and essential FA during the lasT2 mo of pregnancy. Newborn calves were blocked by sex and parity of the dam and assigned randomly to receive 1 of 4 MR treatments (T). Hydrogenated coconut oil and soybean oil were mixed with emulsifier and commercial MR powder to prepare the following 4 MR containing 0.119 and 0.007 (T1), 0.187 and 0.017 (T2), 0.321 and 0.036 (T3), and 0.593 and 0.076 (T4) g of intake per kg of metabolic body weight (BW(0.75)) of linoleic acid and α-linolenic acid, respectively. At 30 d of life, concentrations of essential FA (linoleic acid and α-linolenic acid) in liver increased, whereas concentrations of C12:0, C14:0, C16:0, and C20:3n-9 decreased linearly with increasing intake of essential FA. Body weight gain and feed efficiency were optimized when male calves consumed T2, whereas gain by female calves tended to increase linearly with increasing intake of essential FA during the first 30 d of age. However, these responses to treatment were not maintained after initiation of concentrate feeding at 31 d of life. Over the 60-d preweaning period, wither and hip heights were improved in both sexes as intake of essential FA increased up to T3. Some measures of health and immunity were affected by replacing some coconut oil with soybean oil. Severity of diarrhea tended to decrease linearly; plasma concentrations of haptoglobin during diarrhea were lower in T2, T3, and T4; phagocytosis by blood neutrophils tended to peak for calves fed T2; in vitro proliferation of stimulated blood lymphocytes was greater for calves fed T2; in vitro stimulated blood cells produced more IFN-γ (up to T3 for males and T2 for females), concentrations of serum IgG against ovalbumin injections were increased in males fed T2 or T3; and skin-fold thickness increased in response to an intradermal antigen injection of all calves fed up to T4. Across sex and under the conditions of the present study, mean daily intakes of linoleic acid between 3 to 5g/d and intakes of α-linolenic acid between 0.3 and 0.6g/d during the first 30 d of life promoted growth of preweaned Holstein calves, possibly by improving their immune status.

Regulation of polyunsaturated fatty acid biosynthesis by seaweed fucoxanthin and its metabolite in cultured hepatocytes

The effects of a seaweed carotenoid, fucoxanthin, and its physiological metabolite, fucoxanthinol, on the biosynthesis of polyunsaturated fatty acids (PUFA) were investigated using cultured rat hepatoma BRL-3A. The metabolism of α-linolenic acid (18:3n-3) was suppressed by the addition of these carotenoids, resulting in a decrease in the content of eicosapentaenoic acid (20:5n-3), which suggested a down-regulation of metabolic enzymes such as fatty acid desaturase and elongase. An increase in the content of docosahexaenoic acid (22:6n-3), as observed in previous studies in vivo, might be a buffering action to maintain the membrane fluidity. The suppressive effect of fucoxanthinol on ∆6 fatty acid desaturase was not at the level of gene expression but due to specific modifications of the protein via a ubiquitin-proteasome system. A proteomic analysis revealed several factors such as phosphatidylethanolamine-binding protein that might be involved in the observed action of fucoxanthin. These findings will contribute to studies on the elucidation of the precise molecular mechanisms underlying the regulation of PUFA biosynthesis by fucoxanthin.

Synergism of α-linolenic acid, conjugated linoleic acid and calcium in decreasing adipocyte and increasing osteoblast cell growth

Whole fat milk and dairy products (although providing more energy compared to low- or non-fat products), are good sources of α-linolenic acid (ALA), conjugated linoleic acid (CLA) and calcium, which may be favorable in modulating bone and adipose tissue metabolism. We examined individual and/or synergistic effects of ALA, CLA and calcium (at levels similar to those in whole milk/dairy products) in regulating bone and adipose cell growth. ST2 stromal, MC3T3-L1 adipocyte-like and MC3T3-E1 osteoblast-like cells were treated with: (a) linoleic acid (LNA):ALA ratios = 1-5:1; (b) individual/combined 80-90 % c9, t11 (9,11) and 5-10 % t10, c12 (10,12) CLA isomers; (c) 0.5-3.0 mM calcium; (d) combinations of (a), (b), (c); and (e) control. Local mediators, including eicosanoids and growth factors, were measured. (a) The optimal effect was found at the 4:1 LNA:ALA ratio where insulin-like growth factor-1 (IGF-1) and IGF binding protein-3 (IGFBP-3) production was the lowest in MC3T3-L1 cells. (b) All CLA isomer blends decreased MC3T3-L1 and increased MC3T3-E1 cell differentiation. (c) 1.5-2.5 mM calcium increased ST2 and MC3T3-E1, and decreased MC3T3-L1 cell proliferation. (d) Combination of 4:1 LNA:ALA + 90:10 % CLA + 2.0 mM calcium lowered MC3T3-L1 and increased MC3T3-E1 cell differentiation. Overall, the optimal LNA:ALA ratio to enhance osteoblastogenesis and inhibit adipogenesis was 4:1. This effect was enhanced by 90:10 % CLA + 2.0 mM calcium, indicating possible synergism of these dietary factors in promoting osteoblast and inhibiting adipocyte differentiation in cell cultures.

Fatty acid desaturase 2 (FADS2) insertion/deletion polymorphism impact on muscle fatty acid profile in European grayling (Thymallus thymallus)

An insertion (In)/deletion (Del) polymorphism in the fatty acid desaturase 2 (FADS2) gene, which codes for Δ6-desaturase, was for the first time observed in fish. The polymorphism is located in the seventh intron of FADS2 and the insertion consists of eleven repeats of CTGT (44 bp) with an allelic frequency, for the insertion, of 39 %. The polymorphism was associated with a modulation in Δ6-desaturase activity as significant effects on the ratio of EPA or DHA to their precursors were found (P< 0·001). A different distribution of SFA, MUFA and PUFA among the In/In, In/Del and Del/Del groups was also detected in fish fillet. The results suggest that genetic selection for this marker might improve the ability of European grayling to utilise dietary n-3 long-chain PUFA precursors, as Δ6-desaturase is the rate-limiting enzyme in the production of EPA and DHA from α-linolenic acid.

Homozygous and heterozygous GH transgenesis alters fatty acid composition and content in the liver of Amago salmon (Oncorhynchus masou ishikawae)

Growth hormone (GH) transgenic Amago (Oncorhynchus masou ishikawae), containing the sockeye GH1 gene fused with metallothionein-B promoter from the same species, were generated and the physiological condition through lipid metabolism compared among homozygous (Tg/Tg) and heterozygous GH transgenic (Tg/+) Amago and the wild type control (+/+). Previously, we have reported that the adipose tissue was generally smaller in GH transgenic fish compared to the control, and that the Δ-6 fatty acyl desaturase gene was down-regulated in the Tg/+ fish. However, fatty acid (FA) compositions have not been measured previously in these fish. In this study we compared the FAs composition and content in the liver using gas chromatography. Eleven kinds of FA were detected. The composition of saturated and monounsaturated fatty acids (SFA and MUFA) such as myristic acid (14:0), palmitoleic acid (16:1n-7), and cis-vaccenic acid (cis-18:1n-7) was significantly (P<0.05) decreased in GH transgenic Amago. On the other hand, the composition of polyunsaturated fatty acids (PUFAs) such as linoleic acid (18:2n-6), arachidonic acid (20:4n-6), and docosapentaenoic acid (22:5n-3) was significantly (P<0.05) increased. Levels of serum glucose and triacylglycerol were significantly (P<0.05) decreased in the GH transgenics compared with +/+ fish. Furthermore, 3′-tag digital gene expression profiling was performed using liver tissues from Tg/Tg and +/+ fish, and showed that Mid1 interacting protein 1 (Mid1ip1), which is an important factor to activate Acetyl-CoA carboxylase (ACC), was down-regulated in Tg/Tg fish, while genes involved in FA catabolism were up-regulated, including long-chain-fatty-acid–CoA ligase 1 (ACSL1) and acyl-coenzyme A oxidase 3 (ACOX3). These data suggest that liver tissue from GH transgenic Amago showed starvation by alteration in glucose and lipid metabolism due to GH overexpression. The decrease of serum glucose suppressed Mid1ip1, and caused a decrease of de novo FA synthesis, resulting in a decrease of SFA and MUFA. This induced expression of ACSL1 and ACOX3 to produce energy through β-oxidation in the GH transgenic Amago.

Comprehensive guide to acetyl-carboxylases in algae

Lipids from microalgae have become an important commodity in the last 20 years, biodiesel and supplementing human diets with ω-3 fatty acids are just two of the many applications. Acetyl-CoA carboxylase (ACCase) is a key enzyme in the lipid synthesis pathway. In general, ACCases consist of four functional domains: the biotin carboxylase (BC), the biotin carboxyl binding protein (BCCP), and α-and β-carboxyltransferases (α-and β-CT). In algae, like in plants, lipid synthesis is another function of the chloroplast. Despite being well researched in plants and animals, there is a distinct lack of information about this enzyme in the taxonomically diverse algae. In plastid-containing organisms, ACCases are present in the cytosol and the plastid (chloroplasts) and two different forms exist, the heteromeric (prokaryotic) and homomeric (eukaryotic) form. Despite recognition of the existence of the two ACCase forms, generalized published statements still list the heteromeric form as the one present in algal plastids. In this study, the authors show this is not the case for all algae. The presence of heteromeric or homomeric ACCase is dependent on the origin of plastid. The authors used ACCase amino acid sequence comparisons to show that green (Chlorophyta) and red (Rhodophyta) algae, with the exception of the green algal class Prasinophyceae, contain heteromeric ACCase in their plastids, which are of primary symbiotic origin and surrounded by two envelope membranes. In contrast, algal plastids surrounded by three to four membranes were derived through secondary endosymbiosis (Heterokontophyta and Haptophyta), as well as apicoplast containing Apicomplexa, contain homomeric ACCase in their plastids. Distinctive differences in the substrate binding regions of heteromeric and homomeric α-CT and β-CT were discovered, which can be used to distinguish between the two ACCase types. Furthermore, the acetyl-CoA binding region of homomeric α-CT can be used to distinguish between cytosolic and plastidial ACCase. The information provided here will be of fundamental importance in ACCase expression and activity research to unravel impacts of environmental and physicochemical parameters on lipid content and productivity.

Dietary (n-6 : n-3) fatty acids alter plasma and tissue fatty acid composition in pregnant Sprague Dawley rats

The objective of this paper is to study the effects of varying dietary levels of n-6 : n-3 fatty acid ratio on plasma and tissue fatty acid composition in rat. The treatment groups included control rats fed chow diet only, rats fed 50% soybean oil (SBO): 50% cod liver oil (CLO) (1 : 1), 84% SBO: 16% CLO (6 : 1), 96% SBO: 4% CLO (30 : 1). Blood samples were taken at day 15 of pregnancy, and the plasma and tissue were analyzed for fatty acid profile. The n-3 PUFA in plasma of Diet 1 : 1 group was significantly higher than the other diet groups, while the total n-6 PUFA in plasma was significantly higher in Diet 30 : 1 group as compared to the control and Diet 1 : 1 groups. The Diet 1 : 1 group showed significantly greater percentages of total n-3 PUFA and docosahexaenoic acid in adipose and liver tissue, and this clearly reflected the contribution of n-3 fatty acids from CLO. The total n-6 PUFA, linoleic acid, and arachidonic acid were significantly difference in Diet 30 : 1 as compared to Diet 1 : 1 and control group. These results demonstrated that the dietary ratio of n-6 : n-3 fatty acid ratio significantly affected plasma and tissue fatty acids profile in pregnant rat.

Effect of maternal corticosterone on utilisation of residual yolk sac fatty acids by developing broiler embryo

1. Increased concentrations of maternal corticosterone are deposited into egg yolk under stress conditions. This experiment investigated the effect of maternal corticosterone on yolk and yolk sac fatty acid profiles of eggs and developing broiler embryos. 2. At 42 weeks of age, 200 broiler breeder females were randomly divided into two groups: maternal corticosterone (MC): 2 mg/hen/d of corticosterone dissolved in 1 mL of 99% ethanol and mixed in the individual daily feed for a 14 d period, and control: 1 mL of ethanol added to the individual daily feed. Hens were inseminated, and eggs were collected daily from d 3 of corticosterone feeding to d 14 and incubated. Fatty acid profiles of egg yolk and yolk sac were analysed before incubation and at 12, 14, 18 and 21 d of incubation. 3. Yolk corticosterone concentrations were greater in MC eggs. Before incubation, eggs from MC had lower DHA (22 : 6 n-3) but higher stearic (18 : 0) and dihomo-gamma linolenic (20 : 3 n-6 Cis 8,11,14) acid content compared with the control. 4. Higher concentrations of stearic (18 : 0), elaidic (18 : 1 tr n-9), eicosenoic (20 : 1 n-9), eicosadienoic (20 : 2 n-6), dihomo-gamma linoleic (20 : 3 n-6) and arachidonic (20 : 4 n-6) acids and lower concentrations of myristic (14 : 0), palmitoleic (16 : 1 n-7), linoleic (18 : 2 n-6) and DHA (22 : 6 n-3) were found at different periods of incubation in the residual yolk sac of MC than from controls. 5. The results suggest that the preferentially selective absorption of fatty acids is related to specific tissue requirements.

Highly unsaturated fatty acid synthesis in Atlantic salmon: characterization of ELOVL5- and ELOVL2-like elongases

Fish species vary in their capacity to biosynthesize the n-3 long-chain polyunsaturated fatty acids (LC-PUFA), eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids that are crucial to the health of higher vertebrates. The synthesis of LC-PUFA involves enzyme-mediated fatty acyl desaturation and elongation. Previously, a complementary DNA (cDNA) for an elongase, now termed elovl5a, had been cloned from Atlantic salmon. Here, we report on the cloning of two new elongase cDNAs: a second elovl5b elongase, corresponding to a 294-amino-acid (aa) protein, and an elovl2-like elongase, coding for a 287-aa protein, characterized for the first time in a nonmammalian vertebrate. Heterologous expression in yeast showed that the salmon Elovl5b elongated C18 and C20 PUFA, with low activity towards C22, while Elovl2 elongated C20 and C22 PUFA with lower activity towards C18 PUFA. All three transcripts showed predominant expression in the intestine and liver, followed by the brain. Elongase expression showed differential nutritional regulation. Levels of elovl5b and particularly of elovl2, but not of elovl5a, transcripts were significantly increased in liver of salmon fed vegetable oils (VO) compared to fish fed fish oil (FO). Intestinal expression showed a similar pattern. Phylogenetic comparisons indicate that, in contrast to salmon and zebra fish, Acanthopterygian fish species lack elovl2 which is consistent with their negligible ability to biosynthesize LC-PUFA and to adapt to VO dietary inclusion, compared to predominantly freshwater salmonids. Thus, the presence of elovl2 in salmon explains the ability of this species to biosynthesize LC-PUFA and may provide a biotechnological tool to produce enhanced levels of LC-PUFA, particularly DHA, in transgenic organisms.

OnLine ozonolysis methods for the determination of double bond position in unsaturated lipids

Modern lipidomics relies heavily on mass spectrometry for the structural characterization and quantification of lipids of biological origins. Structural information is gained by tandem mass spectrometry (MS/MS) whereby lipid ions are fragmented to elucidate lipid class, fatty acid chain length, and degree of unsaturation. Unfortunately, however, in most cases double bond position cannot be assigned based on MS/MS data alone and thus significant structural diversity is hidden from such analyses. For this reason, we have developed two online methods for determining double bond position within unsaturated lipids; ozone electrospray ionization mass spectrometry (OzESI-MS) and ozone-induced dissociation (OzID). Both techniques utilize ozone to cleave C-C double bonds that result in chemically induced fragment ions that locate the position(s) of unsaturation.

Effects of dietary n-6:n-3 fatty acid ratio on feed intake, digestibility, and fatty acid profiles of the ruminal contents, liver, and muscle of growing lambs

This study investigated the effect of modifying the n-6:n-3 fatty acid ratio (FAR) of diets using linseed, soybean, and cottonseed oils on apparent digestibility, ruminal fermentation characteristics, growth performance, key circulating hormones, and the fatty acid profile of ruminal digesta, liver, and fore-shank muscle of growing lambs fed a high concentrate diet. Forty individually housed Katadhin Dorper lambs (average of 20.0 kg of BW) were fed Bermudagrass hay in ad libitum amounts and concentrates at 3.7% of BW daily. The concentrate contained 68.9% corn, 23.8% soybean meal, 3.3% limestone, and 4.0% oil supplements (DM basis). The treatments consisted of dietary n-6:n-3 FAR of 2.3:1, 8.8:1, 12.8:1, and 15.6:1. After feeding for 35 d in metabolism crates, lambs were slaughtered 15 h after feeding, and samples of ruminal digesta, blood, liver, and foreshank tissue were collected. Increasing dietary n-6:n-3 FAR did not affect the intake of DM nor the apparent digestibility of DM, ether extract, NDF, or ADF, but did increase apparent digestibility of CP (linear, P < 0.05). Concentrations of ruminal butyrate increased linearly (P < 0.05) with increasing dietary n-6:n-3 FAR, whereas the valerate concentration decreased linearly (P < 0.001). Concentrations of plasma insulin and IGF-I were not affected by dietary n-6:n-3 FAR. Concentrations of C18:3n-3 increased linearly (P < 0.001), whereas that of C18:2n-6 decreased linearly (P < 0.001) in ruminal digesta with decreasing dietary n-6:n-3 FAR. Concentrations of transisomers of fatty acids in ruminal digesta did not change. Proportions of C18:0 in liver and foreshank muscle were unchanged by diet. The proportion of trans11 C18:1 and cis-9 trans11 CLA decreased (P < 0.05) in liver but increased (P < 0.05) in foreshank muscle as dietary n-6:n-3 FAR decreased. Proportions of all measured n-3 fatty acids were greater in liver when diets contained more C18:3n-3 from linseed oil. By decreasing the dietary n-6:n-3 FAR, the proportions of n-6 fatty acids in foreshank muscle decreased dramatically; specifically, C18:2n-6 decreased linearly (P < 0.001) from 28.0 to 16.5% and C20:4n-6 decreased linearly (P < 0.001) from 14.7 to 8.6%. Although feeding a diet that contained more n-3 fatty acids increased the n-3 fatty acid concentration of muscle, the ratio of PUFA to SFA was decreased.

Effect of graded corticosterone treatment on aging-related markers of oxidative stress in rat liver mitochondria

Caloric restriction (CR) decreases aging rate and lowers the rate of reactive oxygen species (ROS) production at mitochondria in different organs, but the signal responsible for this last change is unknown. Glucocorticoids could constitute such a signal since it is well known that their levels increase during CR, and available studies failed to find consistent effects of insulin, the other better described hormone that varies during CR, on mitochondrial oxidative stress. In addition, there is almost no information on the possible in vivo effects of glucocorticoids on specific markers of mitochondrial and tissue oxidative stress. In this investigation, male Wistar rats were treated with corticosterone at doses of 150 and 400 mg/kg of diet during 4 weeks. After that time, oxidative stress-related parameters were measured in the liver. The corticosterone treatments did not change the rate of ROS production or the rate of oxygen consumption of rat liver mitochondria. The two lipoxidation protein markers measured (malondialdehyde-lysine and carboxymethyllysine) were decreased by both corticosterone treatments. These changes were associated with decreases in fatty acid unsaturation, especially with lowered levels of the highly unsaturated araquidonic and docosahexaenoic acids, which decrease the sensitivity to lipid peroxidation processes. The specific protein carbonyl glutamic semialdehyde, a marker of protein oxidation, was also lowered at 400 mg/kg corticosterone. The protein glycoxydation marker carboxyethyllysine and the level of oxidative damage to mtDNA (8-oxo-7,8-dihydro-2 9-deoxyguanosine) were increased by corticosterone. The results do not support the idea that corticosterone is the signal responsible for the decrease in mitochondrial ROS generation during CR. However, they show that this hormone modulates the level of oxidative stress both in proteins and in mtDNA. Some of these changes can contribute to the chronic effects of the hormone at tissue level.

Fatty acids from lipids of marine organisms: molecular biodiversity, roles as biomarkers, biologically active compounds, and economical aspects

Because of their characteristic living environments, marine organisms produce a variety of lipids. Fatty acids constitute the essential part of triglycerides and wax esters, which are the major components of fats and oils. Nevertheless, phospholipids and glycolipids have considerable importance and will be taken into account, especially the latter compounds that excite increasing interest regarding their promising biological activities. Thus, in addition to the major polyunsaturated fatty acids (PUFA) such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, a great number of various fatty acids occur in marine organisms, e.g. saturated, mono- and diunsaturated, branched, halogenated, hydroxylated, methoxylated, non-methylene-interrupted. Various unprecedented chemical structures of fatty acids, and lipid-containing fatty acids, have recently been discovered, especially from the most primitive animals such as sponges and gorgonians. This review of marine lipidology deals with recent advances in the field of fatty acids since the end of the 1990s. Different approaches will be followed, mainly developing biomarkers of trophic chains in marine ecosystems and of chemotaxonomic interest, reporting new structures, especially those with biological activities or biosynthetic interest. An important part of this review will be devoted to the major PUFA, their relevance to health and nutrition, their biosynthesis, their sources (usual and promising) and market.

Molecular cloning and functional characterization of fatty acyl desaturase and elongase cDNAs involved in the production of eicosapentaenoic and docosahexaenoic acids from alpha-linolenic acid in Atlantic salmon (Salmo salar)

Fish are the only major dietary source for humans of omega-3 highly unsaturated fatty acids (HUFAs) and with declining fisheries farmed fish such as Atlantic salmon (Salmo salar) constitute an increasing proportion of the fish in the human diet. However, the current high use of fish oils, derived from wild capture marine fisheries, in aquaculture feeds is not sustainable in the longer term and will constrain continuing growth of aquaculture activities. Greater understanding of how fish metabolize and biosynthesize HUFA may lead to more sustainable aquaculture diets. The study described here contributes to an effort to determine the molecular genetics of the HUFA biosynthetic pathway in salmon, with the overall aim being to determine mechanisms for optimizing the use of vegetable oils in Atlantic salmon culture. In this paper we describe the cloning and functional characterization of 2 genes from salmon involved in the biosynthesis of HUFA. A salmon desaturase complementary DNA, SalDes, was isolated that include an open reading frame of 1362 bp specifying a protein of 454 amino acids. The protein sequence includes all the characteristics of microsomal fatty acid desaturases, including 3 histidine boxes, 2 transmembrane regions, and an N-terminal cytochrome b(5) domain containing a heme-binding motif similar to that of other fatty acid desaturases. Functional expression in the yeast Saccharomyces cerevisiae showed SalDes is predominantly an omega-3 delta5 desaturase, a key enzyme in the synthesis of eicosapentaenoic acid (20:5n-3) from alpha-linolenic acid (18:3n-3). The desaturase showed only low levels of delta6 activity toward C(18) polyunsaturated fatty acids. In addition, a fatty acid elongase cDNA, SalElo, was isolated that included an open reading frame of 888 bp, specifying a protein of 295 amino acids. The protein sequence of SalElo included characteristics of microsomal fatty acid elongases, including a histidine box and a transmembrane region. Upon expression in yeast SalElo showed broad substrate specificity for polyunsaturated fatty acids with a range of chain lengths, with the rank order being C(18) > C(20) > C(22). Thus this one polypeptide product displays all fatty acid elongase activities required for the biosynthesis of docosahexaenoic acid (22:6n-3) from 18:3n-3.

Effects of n-3 polyunsaturated dietary supplementation on the reproductive capacity of male turkeys

To measure the effects of dietary n-3 polyunsaturated fatty acid (PUFA) supplementation on the reproductive capacity of adult male turkeys in industrial flocks, the males of 22 commercial farms were fed either a standard diet or a fish oil diet enriched in n-3 PUFAs. The fatty acid composition of the spermatozoa and reproductive performance were measured throughout the reproductive period. The fish oil diet very effectively increased the percentage of n-3 fatty acids (FA) (22:5n-3 and 22:6n-3) in spermatozoa and correspondingly decreased the percentage of n-6 PUFAs (20:4-6 and 22:4n-6): the n-3/n-6 ratio in spermatozoa fatty acids were 0.04-0.07 with the standard diet and 0.32-0.4 with the fish oil diet. These changes did not affect the spermatozoa content of n-9 PUFAs, particularly of 22:3n-9 which is abundant in turkey spermatozoa (9-12% of the total fatty acids). The supplementation was effective in the middle as at the end of the reproductive period. The reproductive capacity of males was modified by the diet and the positive effect of the n-3 supplemented diet increased with age (increase in hatching rates of nearly 2 points at 48-58 weeks for males fed fish oil diet). These results indicate that an increase in the dietary ratio of n-3/n-6 PUFAs is valuable to sustain the reproductive capacity of male turkeys especially when they are getting older.

Fatty acids of serine, ethanolamine, and choline plasmalogens in some marine bivalves

The FA composition of glycerophospholipid (GPL) classes and subclasses was investigated in whole animals of three marine bivalve mollusks: the Japanese oyster Crassostrea gigas, the blue mussel Mytilus edulis, and the Manila clam Ruditapes philippinarum. Individual organs (gills, mantle, foot, siphon, and muscle) of the Manila clam also were examined. The PS plasmalogen (PSplsm), PE plasmalogen (PEplsm), and PC plasmalogen (PCplsm) subclasses were isolated by HPLC, and their individual FA compositions were examined using GC. Plasmalogen forms of PS and PE, when compared to their respective diacyl forms, were found to be specifically enriched with non-methylene-interrupted (NMI) FA (7,15-22:2, 7,13-22:2, and their precursors) and 20:1 n-11 FA. Such a clear specific association was not found for PCplsm. Interestingly, this trend was most apparent in PSplsm, and the above FA were found to be, respectively, the predominant PUFA and monounsaturated FA in the PSplsm isolated from the three species. This specificity was maintained in all the analyzed organs of the Manila clam but varied in proportions: The highest level of plasmalogens, NMI FA, and 20:1 n-11 was measured in gills and the lowest was in muscle. These results represent the first comprehensive report on a FA composition of the PSplsm subclass isolated from mollusks. The fact that NMI FA and 20:1 n-11, which are thought to be biosynthesized FA, were mainly associated with aminophospholipid plasmalogens (PE and PS) is likely to have a functional significance in bivalve membranes.

Effects of dietary vegetable oil on atlantic salmon hepatocyte fatty acid desaturation and liver fatty acid compositions

Fatty acyl desaturase activities, involved in the conversion of the C18 EFA 18:2n-6 and 18:3n-3 to the highly unsaturated fatty acids (HUFA) 20:4n-6, 20:5n-3, and 22:6n-3, are known to be under nutritional regulation. Specifically, the activity of the desaturation/elongation pathway is depressed when animals, including fish, are fed fish oils rich in n-3 HUFA compared to animals fed vegetable oils rich in C18 EFA. The primary aims of the present study were (i) to establish the relative importance of product inhibition (n-3 HUFA) vs. increased substrate concentration (C18 EFA) and (ii) to determine whether 18:2n-6 and 18:3n-3 differ in their effects on the hepatic fatty acyl desaturation/elongation pathway in Atlantic salmon (Salmo salar). Smolts were fed 10 experimental diets containing blends of two vegetable oils, linseed (LO) and rapeseed oil (RO), and fish oil (FO) in a triangular mixture design for 50 wk. Fish were sampled after 32 and 50 wk, lipid and FA composition of liver determined, fatty acyl desaturation/elongation activity estimated in hepatocytes using [1-14C]18:3n-3 as substrate, and the data subjected to regression analyses. Dietary 18:2n-6 was positively correlated, and n-3 HUFA negatively correlated, with lipid content of liver. Dietary 20:5n-3 and 22:6n-3 were positively correlated with liver FA with a slope greater than unity suggesting relative retention and deposition of these HUFA. In contrast, dietary 18:2n-6 and 18:3n-3 were positively correlated with liver FA with a slope of less than unity suggesting metabolism via beta-oxidation and/or desaturation/elongation. Consistent with this, fatty acyl desaturation/elongation in hepatocytes was significantly increased by feeding diets containing vegetable oils. Dietary 20:5n-3 and 22:6n-3 levels were negatively correlated with hepatocyte fatty acyl desaturation. At 32 wk, 18:2n-6 but not 18:3n-3 was positively correlated with hepatocyte fatty acyl desaturation, whereas the reverse was true at 50 wk. The data indicate that both feedback inhibition through increased n-3 HUFA and decreased C18 fatty acyl substrate concentration are probably important in determining the level of hepatocyte fatty acyl desaturation and that 18:2n-6 and 18:3n-3 may differ in their effects on this pathway.

Food quality controls reproduction of the zebra mussel (Dreissena polymorpha)

Species such as Dreissena polymorpha sometimes contribute substantially in the transfer of primary to secondary production. During the ontogenetic cycle, the reproductive investment of adult mussels is one of the main parameters that affect recruitment success. We studied how food quality and temperature affect the reproductive investment in term of egg mass of D. polymorpha in a lake by sampling mussels monthly from 4 m and 15 m depths. Temperature affected reproduction directly and also indirectly through the food. To assess whether temperature and/or food conditions led to the differences observed in mussels sampled from the two depths, mussels were reared in the laboratory under two different temperature regimes for 3 months, simulating the temperature of the lake at 4 m and 15 m depth. Possible effects of food quality were tested at each temperature using four diets differing in fatty acid composition. Temperature played an important role as a trigger for spawning, and the type of diet clearly affected the reproductive investment. When the heterokont chromophyte alga Nannochloropsis limnetica, which is rich in polyunsaturated fatty acids (PUFAs) and long-chained PUFAs (>C18), was fed to mussels, an increased egg mass was obtained. This result was in contrast to that found when the green alga Scenedesmus obliquus and the cyanobacterium Aphanothece sp., both of which are deficient in long-chained PUFAs, were offered as food to the mussels. Such a PUFA-dependent food quality may affect reproduction in lakes. Food quality effects vary seasonally in a lake and may be most important in summer, when low-food-quality green algae and cyanobacteria are abundant. The low biochemical quality of these blooms may affect at least the later period of gametogenesis of D. polymorpha, which reproduces from June to August.

Evidence of isozymes for delta6 fatty acid desaturase in rat hepatocytes

The expression of delta6 fatty acid desaturase, previously identified, was suppressed almost completely by hyper expression of the corresponding antisense gene in a transformant of the rat hepatic cell line BRL-3A. Conversion rates of [1-14C] linoleic acid, alpha-linolenic acid, and tetracosapentaenoic acid into the respective delta6 fatty acids were equivalent to those in control cells. This finding suggested that all of these reactions were catalyzed by at least two delta6 desaturase isozymes in rat hepatocytes.

Identification and expression of a rat fatty acid elongase involved in the biosynthesis of C18 fatty acids

A major part of the palmitic acid (C16:0) generated by fatty acid synthase is converted into stearic acid (C18:0) via carbon chain elongation. Here, we describe the cloning and expression of a rat hepatic enzyme, rELO2, responsible for the elongation of C16:0, presumably at the condensing reaction. Heterologous expression experiments in a yeast, Saccharomyces cerevisiae, demonstrated the elongation activity of rELO2 on C16:0 and to a lesser extent, C18:0 and fatty acids with low desaturation degree. This was distinct from that rELO1, a rat homolog of HELO1, which preferably catalyzed the elongation of mono- and polyunsaturated fatty acids of C16-C20. The Northern analysis showed that the expression of rELO2, but not rELO1, in hepatocytes was activated by the cycles of fasting and refeeding rats on a fat-free diet. Under these conditions, the rELO1 was expressed constitutively in various tissues but the rELO2 transcripts were detected predominantly in liver.

Delta6-, Stearoyl CoA-, and Delta5-desaturase enzymes are expressed in beta-cells and are altered by increases in exogenous PUFA concentrations

In the evolution of Type II diabetes, an initial period of hyper-fatty acidemia leads to an insulin secretory defect which triggers overt hyperglycemia and frank diabetes. The mechanism by which elevated free fatty acids contribute to beta-cell dysfunction, however, is not clearly understood. We recently reported that arachidonic acid (20:4) or linoleic acid (18:2) supplementations result in increases in abundances of long chain polyunsaturated fatty acids in INS-1 beta-cell membrane lipids, suggesting that beta-cells express desaturases that catalyze generation of unsaturated fatty acids. As expression of desaturases by beta-cells has not yet been addressed, we initiated studies to examine this issue using INS-1 beta-cells and find that they express messages for the Delta6-, stearoyl CoA-, and Delta5-desaturase. Supplementation of the INS-1 beta-cells with arachidonic acid leads to decreased expression of all three desaturases, presumably in response to the decreased need for endogenous generation of unsaturated fatty acids. In contrast, linoleic acid supplementation promoted minimal changes in the three desaturases. These findings demonstrate for the first time that beta-cells express regulatable desaturases. Additionally, reverse transcriptase-polymerase chain reaction analyses reveal expression of the desaturases in native pancreatic islets. It might be speculated that long-term elevations in fatty acids can also adversely influence desaturase activity in beta-cells and affect PUFA composition in beta-cell membranes contributing to beta-cell membrane structural abnormalities and altered secretory function.

Differential induction of stearoyl-CoA desaturase and acyl-CoA oxidase genes by fibrates in HepG2 cells

We studied whether two typical effects of fibrates, induction of stearoyl-CoA desaturase (EC 1.14.99.5) and peroxisome proliferation, are related. The effect of bezafibrate on the activity and mRNA of stearoyl-CoA desaturase and acyl-CoA oxidase in the liver and epididymal white adipose tissue of male Sprague-Dawley rats was determined. The same parameters were measured in HepG2 cells, a cell line resistant to peroxisome proliferation, following incubation with ciprofibrate. Bezafibrate increased the hepatic mRNA levels (14.5-fold on day 7) and activity (9.3-fold on day 15) of acyl-CoA oxidase. Stearoyl-CoA desaturase mRNA levels were transiently increased (2.7-fold on day 7), while its activity remained increased at the end of the treatment (2.4-fold). In white adipose tissue, bezafibrate increased the mRNA (5-fold) and activity (1.9-fold) of acyl-CoA oxidase, while stearoyl-CoA desaturase was not modified. Ciprofibrate addition to HepG2 cells cultured in 7% fetal bovine serum (FBS) only increased the stearoyl-CoA desaturase mRNA (1.9-fold). When cells were cultured in 0.5% FBS, ciprofibrate increased acyl-CoA oxidase mRNA (2.2-fold), while the increase in stearoyl-CoA desaturase mRNA was identical (1.9-fold). Further, its activity was also increased (1.5-fold). Incubation of HepG2 cells in the presence of cycloheximide did not alter the capacity of ciprofibrate to induce stearoyl-CoA desaturase mRNA, whereas the presence of actinomycin abolished the induction. In addition, preincubation of HepG2 cells with ciprofibrate increased the rate of stearoyl-CoA desaturase mRNA degradation. The results presented in this study suggest that fibrates induce stearoyl-CoA desaturase activity and mRNA levels independently of peroxisome proliferation.

Elo1p-dependent carboxy-terminal elongation of C14:1Delta(9) to C16:1Delta(11) fatty acids in Saccharomyces cerevisiae

Saccharomyces cerevisiae medium-chain acyl elongase (ELO1) mutants have previously been isolated in screens for fatty acid synthetase (FAS) mutants that fail to grow on myristic acid (C14:0)-supplemented media. Here we report that wild-type cells cultivated in myristoleic acid (C14:1Delta(9))-supplemented media synthesized a novel unsaturated fatty acid that was identified as C16:1Delta(11) fatty acid by gas chromatography-mass spectroscopy. Synthesis of C16:1Delta(11) was dependent on a functional ELO1 gene, indicating that Elo1p catalyzes carboxy-terminal elongation of unsaturated fatty acids (alpha-elongation). In wild-type cells, the C16:1Delta(11) elongation product accounted for approximately 12% of the total fatty acids. This increased to 18% in cells that lacked a functional acyl chain desaturase (ole1Delta mutants) and hence were fully dependent on uptake and elongation of C14:1. The observation that ole1Delta mutant cells grew almost like wild type on medium supplemented with C14:1 indicated that uptake and elongation of unsaturated fatty acids were efficient. Interestingly, wild-type cells supplemented with either C14:1 or C16:1 fatty acids displayed dramatic alterations in their phospholipid composition, suggesting that the availability of acyl chains is a dominant determinant of the phospholipid class composition of cellular membranes. In particular, the relative content of the two major phospholipid classes, phosphatidylethanolamine and phosphatidylcholine, was strongly dependent on the chain length of the supplemented fatty acid. Moreover, analysis of the acyl chain composition of individual phospholipid classes in cells supplemented with C14:1 revealed that the relative degree of acyl chain saturation characteristic for each phospholipid class appeared to be conserved, despite the gross alteration in the cellular acyl chain pool. Comparison of the distribution of fatty acids that were taken up and elongated (C16:1Delta(11)) to those that were endogenously synthesized by fatty acid synthetase and then desaturated by Ole1p (C16:1Delta(9)) in individual phospholipid classes finally suggested the presence of two different pools of diacylglycerol species. These results will be discussed in terms of biosynthesis of different phospholipid classes via either the de novo or the Kennedy pathway.

Electrospray ionization mass spectrometric analyses of phospholipids from INS-1 insulinoma cells: comparison to pancreatic islets and effects of fatty acid supplementation on phospholipid composition and insulin secretion

Insulin secretion by pancreatic islet beta-cells is impaired in diabetes mellitus, and normal beta-cells are enriched in phospholipids with arachidonate as sn-2 substituent. Such molecules may play structural roles in exocytotic membrane fusion or serve as substrates for phospholipases activated by insulin secretagogues. INS-1 insulinoma cells respond to secretagogues and permit the study of effects of culture with free fatty acids on phospholipid composition and secretion. INS-1 cell glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE) lipids are demonstrated here by electrospray ionization mass spectrometry to contain a lower fraction of molecules with arachidonate and a higher fraction with oleate as sn-2 substituent than native islets. Palmitic acid supplementation induces little change in these INS-1 cell lipids, but supplementation with linoleate or arachidonate induces a large rise in the fraction of INS-1 cell GPC species with polyunsaturated sn-2 substituents and a fall in oleate-containing species to yield a GPC profile similar to native islets. The fraction of GPE lipids comprised of plasmenylethanolamine species with polyunsaturated sn-2 substituents in early-passage INS-1 cells is similar to that of islets, but declines on serial passage. Such molecules might participate in exocytotic membrane fusion, and late-passage INS-1 cells have reduced insulin secretory responses. Arachidonate supplementation induces a rise in the fraction of INS-1 cell GPE lipids with polyunsaturated sn-2 substituents and partially restores responses to insulin secretagogues by late-passage INS-1 cells, but does not further amplify secretion by early-passage cells. Effects of extracellular free fatty acids on beta-cell phospholipid composition and secretory responses could be involved in changes in beta-cell function during the period of hyper-free fatty acidemia that precedes diabetes mellitus.

13C NMR study of the effects of leptin treatment on kinetics of hepatic intermediary metabolism

The recent discovery of leptin receptors in peripheral tissue raises questions about which of leptin's biological actions arise from direct effects of the hormone on extraneural tissues and what intracellular mechanisms are responsible for leptin's effects on carbohydrate and lipid metabolism. The present study is focused on the action of leptin on hepatic metabolism. Nondestructive 13C NMR methodology was used to follow the kinetics of intermediary metabolism by monitoring flux of 13C-labeled substrate through several multistep pathways. In perfused liver from either ob/ob or lean mice, we found that acute treatment with leptin in vitro modulates pathways controlling carbohydrate flux into 13C-labeled glycogen, thereby rapidly enhancing synthesis by an insulin-independent mechanism. Acute treatment of ob/ob liver also caused a rapid stimulation of long-chain fatty acid synthesis from 13C-labeled acetyl-CoA by the de novo synthesis route. Chronic leptin treatment in vivo induced homeostatic changes that resulted in a tripling of the rate of glycogen synthesis via the gluconeogenic pathway from [2-13C]pyruvate in ob/ob mouse liver perfused in the absence of the hormone. Consistent with the 13C NMR results, leptin treatment of the ob/ob mouse in vivo resulted in significantly increased hepatic glycogen synthase activity. Chronic treatment with leptin in vivo exerted the opposite effect of acute treatment in vitro and markedly decreased hepatic de novo synthesis of fatty acids in ob/ob mouse liver. In agreement with the 13C NMR findings, activities of hepatic acetyl-CoA carboxylase and fatty acid synthase were significantly reduced by chronic treatment of the ob/ob mouse with leptin. Our data represent a demonstration of direct effects of leptin in the regulation of metabolism in the intact functioning liver.

Low-dose eicosapentaenoic or docosahexaenoic acid administration modifies fatty acid composition and does not affect susceptibility to oxidative stress in rat erythrocytes and tissues

In view of the promising future for use of n-3 polyunsaturated fatty acids (PUFA) in the prevention of cancer and cardiovascular diseases, it is necessary to ensure that their consumption does not result in detrimental oxidative effects. The aim of the present work was to test a hypothesis that low doses of eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) do not induce harmful modifications of oxidative cell metabolism, as modifications of membrane fatty acid composition occur. Wistar rats received by gavage oleic acid, EPA, or DHA (360 mg/kg body weight/day) for a period of 1 or 4 wk. Fatty acid composition and alpha-tocopherol content were determined for plasma, red blood cell (RBC) membranes, and liver, kidney, lung, and heart microsomal membranes. Susceptibility to oxidative stress induced by tert-butylhydroperoxide was measured in RBC. EPA treatment increased EPA and docosapentaenoic acid (DPA) content in plasma and in all the membranes studied. DHA treatment mainly increased DHA content. Both treatments decreased arachidonic acid content and n-6/n-3 PUFA ratio in the membranes, without modifying the Unsaturation Index. No changes in tissue alpha-tocopherol content and in RBC susceptibility to oxidative stress were induced by either EPA or DHA treatment. The data suggest that EPA and DHA treatments can substantially modify membrane fatty acids, without increasing susceptibility to oxidative stress, when administered at low doses. This opens the possibility for use of low doses of n-3 PUFA for chemoprevention without risk of detrimental secondary effects.