Hepatic and plasma sex differences in saturated and monounsaturated fatty acids are associated with differences in expression of elongase 6, but not stearoyl-CoA desaturase in Sprague-Dawley rats

Circulating fatty acids and risk of severe non-alcoholic fatty liver disease in the UK biobank: a prospective cohort of 116 223 individuals

Fatty acid (FA) metabolism plays an important role in the development of nonalcoholic fatty liver disease (NAFLD). However, data on the relationship between circulating FAs and NAFLD risk are limited. This study aims to assess the associations between specific circulating FAs and severe NAFLD risk among the general population. Overall 116 223 participants without NAFLD and other liver diseases from the UK Biobank were enrolled between 2006 and 2010 and were followed up until the end of 2021. Plasma concentrations of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs) were analyzed using an NMR-based biomarker profiling platform. Hazard ratios (HRs) and 95% confidence intervals (CIs) of NAFLD risk were estimated using Cox proportional-hazard models adjusted for other potential confounders. During a mean follow-up of 12.3 years, we documented 1394 cases of severe NAFLD. After multivariate adjustment, plasma SFAs and MUFAs were associated with a higher risk of severe NAFLD, whereas plasma n-3 PUFAs, n-6 PUFAs, and linoleic acid (LA) were associated with a lower risk. As compared with the lowest quartile, HRs (95% CIs) of severe NAFLD risk in the highest quartiles were 1.85 (1.45-2.36) for SFAs, 1.74 (1.23-2.44) for MUFAs, 0.79 (0.65-0.97) for n-3 PUFAs, 0.68 (0.48-0.96) for n-6 PUFAs, and 0.73 (0.54-0.99) for LA. The significant relationships were mainly mediated by serum TG for SFAs, HDL-C for MUFAs and n-6 PUFAs, and C-reactive protein for n-3 PUFAs. Plasma SFAs were associated with a more pronounced increase in the risk of severe NAFLD among participants with fewer SFA-associated alleles (P interaction = 0.032). Dietary recommendations for reducing plasma SFAs and MUFAs while increasing n-3 and n-6 PUFAs may be protective for severe NAFLD, which could be mediated by lipid metabolism and inflammation.

Sex- and enantiospecific differences in the formation rate of hydroxyeicosatetraenoic acids in rat organs

Hydroxyeicosatetraenoic acids (HETEs) are hydroxylated arachidonic acid (AA) metabolites that are classified into midchain, subterminal, and terminal HETEs. Hydroxylation results in the formation of R and S enantiomers for each HETE, except for 20-HETE. HETEs have multiple physiological and pathological effects. Several studies have demonstrated sex-specific differences in AA metabolism in different organs. In this study, microsomes from the heart, liver, kidney, lung, intestine, and brain of adult male and female Sprague-Dawley rats were isolated and incubated with AA. Thereafter, the enantiomers of all HETEs were analyzed by liquid chromatography-tandem mass spectrometry. We found significant sex- and enantiospecific differences in the formation levels of different HETEs in all organs. The majority of HETEs, especially midchain HETEs and 20-HETE, showed significantly higher formation rates in male organs. In the liver, the R enantiomer of several HETEs showed a higher formation rate than the corresponding S enantiomer (e.g., 8-, 9-, and 16-HETE). On the other hand, the brain and small intestine demonstrated a higher abundance of the S enantiomer. 19(S)-HETE was more abundant than 19(R)-HETE in all organs except the kidney. Elucidating sex-specific differences in HETE levels provides interesting insights into their physiological and pathophysiological roles and their possible implications for different diseases.

Sex differences in hippocampal-dependent memory and the hippocampal lipidome in adolescent rats raised on diets with or without DHA

Recent studies suggest the effects of DHA supplementation on human memory may differ between females and males during infancy, adolescence, and early adulthood, but the underlying mechanisms are not clear. As a result, this study sought to examine the spatial memory and brain lipidomic profiles in female and male adolescent rats with or without a DHA-enriched diet that began perinatally with the supplementation of dams. Spatial learning and memory were examined in adolescent rats using the Morris Water Maze beginning at 6 weeks of age and animals were sacrificed at 7 weeks of age to permit isolation of brain tissue and blood samples. Behavioral testing showed that there was a significant diet x sex interaction for two key measures of spatial memory (distance to zone and time spent in the correct quadrant during the probe test), with female rats benefiting the most from DHA supplementation. Lipidomic analyses suggest levels of arachidonic acid (ARA) and n-6 docosapentaenoic acid (DPA) containing phospholipid species were lower in the hippocampus of DHA supplemented compared with control animals, and principal component analyses revealed a potential dietary treatment effect for hippocampal PUFA. Females fed DHA had slightly more PE P-18:0_22:6 and maintained levels of PE 18:0_20:4 in the hippocampus in contrast with males fed DHA. Understanding how DHA supplementation during the perinatal and adolescent periods changes cognitive function in a sex-specific manner has important implications for determining the dietary requirements of DHA. This study adds to previous work highlighting the importance of DHA for spatial memory and provides evidence that further research needs to consider how DHA supplementation can cause sex-specific changes.

Characterisation of the Paternal Influence on Intergenerational Offspring Cardiac and Brain Lipid Homeostasis in Mice

There is growing evidence that poor paternal diet at the time of conception increase the risk of offspring developing a range of non-communicable metabolic diseases, such as obesity, diabetes and cardiovascular disease, in adulthood. We hypothesise that a paternal low protein-high carbohydrate diet perturbs offspring tissue lipid abundance through both sperm and seminal plasma-mediated mechanisms. To test our hypothesis, we fed male C57BL/6 mice either a control normal protein diet (NPD; 18% protein) or an isocaloric low protein diet (LPD; 9% protein) for a minimum of 8 weeks. We generated offspring through artificial insemination, in combination with vasectomised male mating. Using this approach, we derived offspring from either NPD or LPD sperm but in the presence of NPD or LPD seminal plasma. Using high resolution mass-spectrometry, we found that offspring derived from either LPD sperm or seminal fluid displayed perturbed cardiac and brain lipid abundance from just three weeks of age, typically associated with the altered abundance of tissue triglycerides. We also observed the differential sex-specific patterns of lipids between the control and experimental offspring's hearts and brains. These observations indicate that poor paternal diet at the time of conception affects offspring cardiac and brain lipid profiles in an age-, sex- and generation-specific manner.

Molecular programming modulates hepatic lipid metabolism and adult metabolic risk in the offspring of obese mothers in a sex-specific manner

Male and female offspring of obese mothers are known to differ extensively in their metabolic adaptation and later development of complications. We investigate the sex-dependent responses in obese offspring mice with maternal obesity, focusing on changes in liver glucose and lipid metabolism. Here we show that maternal obesity prior to and during gestation leads to hepatic steatosis and inflammation in male offspring, while female offspring are protected. Females from obese mothers display important changes in hepatic transcriptional activity and triglycerides profile which may prevent the damaging effects of maternal obesity compared to males. These differences are sustained later in life, resulting in a better metabolic balance in female offspring. In conclusion, sex and maternal obesity drive differently transcriptional and posttranscriptional regulation of major metabolic processes in offspring liver, explaining the sexual dimorphism in obesity-associated metabolic risk.

Sex and maternal obesity drive differently transcriptional and posttranscriptional regulation of major metabolic processes in the livers of female and male offspring, contributing to the sexual dimorphism in obesity-associated metabolic risk.

The repertoire of the elongation of very long-chain fatty acids (Elovl) protein family is conserved in tambaqui (Colossoma macropomum): Gene expression profiles offer insights into the sexual differentiation process

Elongation of very long-chain fatty acids (Elovl) proteins are critical players in the regulation of the length of a fatty acid. At present, eight members of the Elovl family (Elovl1-8), displaying a characteristic fatty acid substrate specificity, have been identified in vertebrates, including teleost fish. In general, Elovl1, Elovl3, Elovl6 and Elovl7 exhibit a substrate preference for saturated and monounsaturated fatty acids, while Elovl2, Elovl4, Elovl5 and Elovl8 use polyunsaturated fatty acids (PUFA) as substrates. PUFA elongases have received considerable attention in aquatic animals due to their involvement in the conversion of C₁₈ PUFAs to long-chain polyunsaturated fatty acids (LC-PUFA). Here, we identified the full repertoire of elovl genes in the tambaqui Colossoma macropomum genome. A detailed phylogenetic and synteny analysis suggests a conservation of these genes among teleosts. Furthermore, based on RNAseq gene expression data, we discovered a gender bias expression of elovl genes during sex differentiation of tambaqui, toward future males. Our findings suggest a role of Elovl enzymes and fatty acid metabolism in tambaqui sexual differentiation.

Circulating Fatty Acids and Genetic Predisposition to Type 2 Diabetes: Gene-Nutrient Interaction Analysis

OBJECTIVE

To assess the relationship of circulating fatty acids (FA) with risk of type 2 diabetes (T2D) and potential interactions with genetic risk.

RESEARCH DESIGN AND METHODS

A total of 95,854 participants with complete data on plasma FA from the UK Biobank were enrolled between 2006 and 2010 and were followed up to the end of 2020. Plasma concentrations of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) were analyzed by a high-throughput nuclear magnetic resonance-based biomarker profiling platform. The genetic risk scores (GRS) were calculated on the basis of 424 variants associated with T2D. Pathway-specific GRS were calculated based on robust clusters of T2D loci.

RESULTS

There were 3,052 instances of T2D documented after an average follow-up of 11.6 years. Plasma concentrations of SFA and MUFA were positively associated with T2D risk, while plasma PUFA were inversely associated. After adjustment for major risk factors, hazard ratios (95% CI) of T2D for 1-SD increment were 1.03 (1.02-1.04) for SFA, 1.03 (1.02-1.05) for MUFA, 0.62 (0.56-0.68) for PUFA, 0.67 (0.61-0.73) for n-6 PUFA, 0.90 (0.85-0.95) for n-3 PUFA, and 1.01 (0.98-1.04) for n-6-to-n-3 ratio. Plasma MUFA had significant interactions with the overall GRS and GRS for proinsulin and liver/lipid clusters on T2D risk. The protective associations of n-3 PUFA with T2D risk were weaker among individuals with higher obesity GRS (P interaction = 0.040) and liver/lipid GRS (P interaction = 0.012). Additionally, increased plasma n-3 PUFA concentration was associated with more reductions in T2D risk among participants carrying more docosapentaenoic acid-associated alleles (P interaction = 0.007).

CONCLUSIONS

Plasma concentrations of SFA and MUFA were associated with a higher T2D risk, whereas plasma PUFA and n-6 and n-3 PUFA were related to a lower risk. Circulating MUFA and n-3 PUFA had significant interactions with genetic predisposition to T2D and FA-associated variants.

Testosterone Deficiency Promotes Hypercholesteremia and Attenuates Cholesterol Liver Uptake via AR/PCSK9/LDLR Pathways

BACKGROUND

Testosterone deficiency is reportedly correlated with an elevation of cholesterol in plasma, but the mechanism remains unclear. Our objective was to investigate the effects of testosterone deficiency on cholesterol metabolism and the corresponding molecular changes in vivo and in vitro.

METHODS

SD rats were randomized into three groups: sham-operated (SHAM), subtotal orchiectomized (SO), and orchiectomized (ORX) and fed for 8 weeks. HepG2 cells were cultured with medium containing testosterone with the final concentrations of 0, 10, 30, and 300 nM. Method of isotope tracing and fluorescence labelling was adopted to investigate cholesterol metabolism. Several key molecules of cholesterol metabolism were also analyzed.

RESULTS

SO and ORX rats displayed dysfunctional liver uptake of cholesterol. HepG2 cells incubated with testosterone of lower and excessive level exhibited reduced capacity of cholesterol uptake. Further investigation revealed that lack of testosterone induced increased proprotein convertase subtilisin/kexin type 9 (PCSK9) and decreased low-density lipoprotein receptor (LDLR) both in vivo and in vitro. Moreover, the androgen receptor (AR) antagonist flutamide mimicked the effects of testosterone deficiency on PCSK9 and LDLR indicating the role of AR as a mediator in triggering attenuating liver cholesterol uptake in which testosterone instead of dihydrotestosterone (DHT) is the major functional form of androgen.

CONCLUSION

Testosterone deficiency attenuated cholesterol liver uptake mediated by the PCSK9-LDLR pathway, in which AR and testosterone without transforming to DHT play important roles.

Characterization of a novel FADS2 transcript variant: implications for D6D activity regulation in cells

Delta-6-desaturase (D6D) activity is deficient in MCF-7 and other cancer cell lines, but it is not explained by FADS2 gene mutations. This deficient activity was not ameliorated by induction of the FADS2 gene; therefore, we hypothesized that some of the induced FADS2 transcript variants (tv) may play a negative regulatory role. FADS2_tv1 is the reference FADS2 tv, coding for full-length D6D isoform 1 (D6D-iso1), and alternative transcriptional start sites result in FADS2_tv2 and FADS2_tv3 variants encoding D6D-iso2 and D6D-iso3 isoforms, respectively, which lack the catalytically critical N-terminal domain. In MCF-7 cells, FADS2_tv2 and FADS2_tv3 were expressed at significantly higher levels than FADS2_tv1. Overexpression of FADS2_tv2 in HEK293 cells confirmed that D6D-iso2 is non-functional, and co-transfection demonstrated a dominant-negative role for D6D-iso2 in D6D-iso1 activity regulation. FADS2_tv2 was expressed at higher levels than FADS2_tv1 in HeLa, MDA-MB-435, MCF-10 A, and HT-29 cells, but at lower levels in A549, MDA-MB-231, and LNCaP cells. Overexpression studies indicated roles for FADS2 variants in proliferation and apoptosis regulation, which were also cell-line specific. Increased FADS2_tv2 expression provides a new mechanism to help explain deficient D6D activity in MCF-7 and other cancer cell lines, but it is not a hallmark of malignant cells.

β-Carotene Bioavailability and Conversion Efficiency Are Significantly Affected by Sex in Rats: First Observation Suggesting a Possible Hormetic Regulation of Vitamin A Metabolism in Female Rats

SCOPE

To study the effect of variation in dietary vitamin A (VA) content on its hepatic and intestinal metabolism.

METHODS AND RESULTS

Adult female and male rats are fed with diets containing 400, 2300, or 9858 IU kg^-1 VA for 31-33 weeks. VA concentrations are measured in plasma and liver. Bioavailability and intestinal conversion efficiency of β-carotene to VA are assessed by measuring postprandial plasma β-carotene and retinyl palmitate concentrations after force-feeding rats with β-carotene. Expression of genes involved in VA metabolism, together with concentrations of RBP4, BCO1, and SR-BI proteins, are measured in the intestine and liver of female rats. Plasma retinol concentrations are lower and hepatic free retinol concentrations are higher in females than in males. There is no effect of dietary VA content on β-carotene bioavailability and its conversion efficiency, but bioavailability is higher and conversion efficiency is lower in females than in males. The expression of most genes exhibited a U-shaped dose response curve depending on VA intake.

CONCLUSIONS

β-Carotene bioavailability and conversion efficiency to VA are affected by the sex of rats. Results of gene expression suggest a hormetic regulation of VA metabolism in female rats.

Administration of ursolic acid to new-born pups prevents dietary fructose-induced non-alcoholic fatty liver disease in Sprague Dawley rats

Overconsumption of fructose time dependently induces the development of non-alcoholic fatty liver disease (NAFLD). We investigated whether ursolic acid (UA) intake by new-born rats would protect against fructose-induced NAFLD. One hundred and seven male and female Sprague Dawley rat pups were randomly grouped and gavaged (10 ml/kg body weight) with either 0.5% dimethylsulphoxide (vehicle control), 0.05% UA, 50% fructose mixed with UA (0.05%) or 50% fructose alone, from postnatal day 6 (P6) to P20. Post-weaning (P21-P69), the rats received normal rat chow (NRC) and water to drink. On P70, the rats in each group were continued on water or 20% fructose to drink, as a secondary high fructose diet during adulthood. After 8 weeks, body mass, food and fluid intake, circulating metabolites, visceral adiposity, surrogate markers of liver function and indices of NAFLD were determined. Food intake was reduced as a result of fructose feeding in both male and female rats (p < 0.0001). Fructose consumption in adulthood significantly increased fluid intake and visceral adiposity in female rats (p < 0.05) and had no apparent effects in male rats (p > 0.05). In both sexes of rats, fructose had no significant (p > 0.05) effects on body mass, circulating metabolites, total calorie intake and surrogate markers of hepatic function. Fructose consumption in both early life and adulthood in female rats promoted hepatic lipid accumulation (p < 0.001), hypertrophy, microvesicular and macrovesicular steatosis (p < 0.05). Early-life UA intake significantly (p < 0.001) reduced fructose-induced hepatic lipid accumulation in both male and female rats. Administration of UA during periods of developmental plasticity shows prophylactic potential against dietary fructose-induced NAFLD.

Brain PUFA Concentrations Are Differentially Affected by Interactions of Diet, Sex, Brain Regions, and Phospholipid Pools in Mice

BACKGROUND

PUFAs play vital roles in the development, maintenance, and functioning of circuitries that regulate reward and social behaviors. Therefore, modulations in PUFA concentrations of these brain regions may disrupt reward and social circuitries contributing to mood disorders, developmental disabilities, and addictions. Though much is known about regional and phospholipid-pool-specific PUFA concentrations, less is known about the effects of dietary interventions that concurrently lowers n-6 PUFA and supplements n-3 PUFA, on brain PUFA concentrations. There is even less knowledge on the effects of sex on brain PUFA concentrations.

OBJECTIVE

This study aimed to comprehensively examine the interaction effects of diet (D), sex (S), brain regions (BR), and phospholipid pools (PL) on brain PUFA concentrations.

METHODS

Male and female C57BL/6J mice were fed 1 of 4 custom-designed diets varying in linoleic acid (LNA) (8 en% or 1 en%) and eicosapentaenoic acid/docosahexaenoic acid (EPA/DHA) (0.4 en% or 0 en%) concentrations from in utero to 15 weeks old. At 15 weeks old, the prefrontal cortex, dorsal striatum, and cerebellum were collected. Fatty acids of 5 major PL were quantified by GC-flame ionization detection. Repeated measures ANOVA was used to test for differences among the groups for D, S, BR, and PL.

RESULTS

No significant 4-way interactions on PUFA concentrations. DHA, predominant n-3 PUFA, concentrations were dependent on significant D × BR × PL interactions. DHA concentration was not affected by sex. Arachidonic acid (ARA; predominant n-6 PUFA) concentrations were not dependent on 3-way interactions. However, significant 2-way D × PL, BR × PL, and D × Sinteractions affected ARA concentrations. Brain fatty acid concentrations were differentially affected by various combinations of D, S, BR, and PL interactions.

CONCLUSION

Though DHA concentrations are not affected by sex, ARA concentrations are affected by interactions of the 4 variables examined. This study provides comprehensive references in the investigation of complex interactions between factors that affect brain PUFA concentrations in mice.

Effects of algae supplementation in high-energy dietary on fatty acid composition and the expression of genes involved in lipid metabolism in Hu sheep managed under intensive finishing system

This study aims to investigate the effect of algae supplementation in high-energy diet (HE diet) on lipid metabolism of intensive feeding sheep. The lambs were assigned to two groups and received a standard diet (ST diet, 8.40 MJ/kg) or a HE diet (9.70 MJ/kg) based on corn, wheat bran, soybean meal. Each group was divided into two subgroups: control and algae supplement (3%, DM basis). The body fat, serum cholesterol, and oleic acid in the liver and muscle increased in lambs receiving the HE diet. However, after supplementing the microalgae (Schizochytrium sp.) in the HE diet, these parameters were all reduced. In addition, EPA, DHA and CLA cis-9, trans-11 in muscle and liver increased. Algae supplementation also altered the expression of lipid metabolism-related genes, including up-regulated FADS2, ELOVL2, SCD, CPT1α and SREBF-1, and down-regulated PPARα and PPARγ. In conclusion, algae supplementation in ST and HE diets increased n-3PUFA and improved metabolic disorder caused by the HE diet.

Sex-based differences in hepatic and skeletal muscle triglyceride storage and metabolism 1

Women and men store lipid differently within the body with men storing more fat in the android region and women storing more fat in the gynoid region. Fat is predominately stored in adipose tissue as triacylglycerides (TG); however, TG are also stored in other tissues including the liver and skeletal muscle. Excess hepatic TG storage, defined as a TG concentration >5% of liver weight and known as nonalcoholic fatty liver disease (NAFLD), is related to the metabolic syndrome. Similarly, elevated skeletal muscle TG, termed intramyocellular lipids (IMCL), are related to insulin resistance in obesity and type II diabetes. Men store more hepatic TG than women and, unsurprisingly, NAFLD is more prevalent in men than women. Women store more IMCL than men, yet type II diabetes risk is not greater, which is likely due to the manner in which women store TG within muscle. Sex-based differences in TG storage between men and women are underpinned by differences in messenger RNA expression, protein content, and enzyme activities of skeletal muscle and hepatic lipid metabolic pathways. Furthermore, women have a greater reliance on lipid during exercise because of upregulation of lipid oxidative pathways. The purpose of this review is to discuss the role of sex in mediating lipid storage and metabolism within skeletal muscle and the liver at rest and during exercise and its relationship with metabolic disease.

Impact of estrogens and estrogen receptor-α in brain lipid metabolism

Estrogens and their receptors play key roles in regulating body weight, energy expenditure, and metabolic homeostasis. It is known that lack of estrogens promotes increased food intake and induces the expansion of adipose tissues, for which much is known. An area of estrogenic research that has received less attention is the role of estrogens and their receptors in influencing intermediary lipid metabolism in organs such as the brain. In this review, we highlight the actions of estrogens and their receptors in regulating their impact on modulating fatty acid content, utilization, and oxidation through their direct impact on intracellular signaling cascades within the central nervous system.

PEMT, Δ6 desaturase, and palmitoyldocosahexaenoyl phosphatidylcholine are increased in rats during pregnancy

DHA is important for fetal neurodevelopment. During pregnancy, maternal plasma DHA increases, but the mechanism is not fully understood. Using rats fed a fixed-formula diet (DHA as 0.07% total energy), plasma and liver were collected for fatty acid profiling before pregnancy, at 15 and 20 days of pregnancy, and 7 days postpartum. Phosphatidylethanolamine methyltransferase (PEMT) and enzymes involved in PUFA synthesis were examined in liver. Ad hoc transcriptomic and lipidomic analyses were also performed. With pregnancy, DHA increased in liver and plasma lipids, with a large increase in plasma DHA between day 15 and day 20 that was mainly attributed to an increase in 16:0/DHA phosphatidylcholine (PC) in liver (2.6-fold) and plasma (3.9-fold). Increased protein levels of Δ6 desaturase (FADS2) and PEMT at day 20 and increased Pemt expression and PEMT activity at day 15 suggest that during pregnancy, both DHA synthesis and 16:0/DHA PC synthesis are upregulated. Transcriptomic analysis revealed minor changes in the expression of genes related to phospholipid synthesis, but little insight on DHA metabolism. Hepatic PEMT appears to be the mechanism for increased plasma 16:0/DHA PC, which is supported by increased DHA biosynthesis based on increased FADS2 protein levels.

Sexual dimorphism in hepatic lipids is associated with the evolution of metabolic status in mice

Ectopic lipid accumulation in the liver is implicated in metabolic disease in an age- and sex-dependent manner. The role of hepatic lipids has been well established within the scope of metabolic insults in mice, but has been insufficiently characterized under standard housing conditions, where age-related metabolic alterations are known to occur. We studied a total of 10 male and 10 female mice longitudinally. At 3, 7 and 11 months of age, non-invasive ¹ H-magnetic resonance spectroscopy (¹ H-MRS) was used to monitor hepatic lipid content (HLC) and fatty acid composition in vivo, and glucose homeostasis was assessed with glucose and insulin challenges. At the end of the study, hepatic lipids were comprehensively characterized by nuclear magnetic resonance (NMR) and liquid chromatography-mass spectrometric analyses of liver tissue samples. In males, HLC increased from 1.4 ± 0.1% at 3 months to 2.9 ± 0.3% at 7 months (p < 0.01) and 2.7 ± 0.3% at 11 months (p < 0.05), in correlation with fasting insulin levels (p < 0.01, r = 0.51) and parameters from the insulin tolerance test (ITT; p < 0.001, r = -0.69 versus area under the curve; p < 0.01, r = -0.57 versus blood glucose drop at 1 h post-ITT; p < 0.01, r = 0.55 versus blood glucose at 3 h post-ITT). The metabolic performance of females remained the same throughout the study, and HLC was higher than that of males at 3 months (2.7 ± 0.2%, p < 0.01), but comparable at 7 months (2.2 ± 0.2%) and 11 months (2.2 ± 0.1%). Strong sexual dimorphism in bioactive lipid species, including diacylglycerols (higher in males, p < 0.0001), phosphatidylinositols (higher in females, p < 0.001) and omega-3 polyunsaturated fatty acids (higher in females, p < 0.01), was found to be in good correlation with metabolic scores at 11 months. Therefore, in mice housed under standard conditions, sex-specific composition of bioactive lipids is associated with metabolic protection in females, whose metabolic performance was independent of hepatic cytosolic lipid content.

Effects of different dietary DHA:EPA ratios on gonadal steroidogenesis in the marine teleost, tongue sole (Cynoglossus semilaevis)

The present study was conducted to investigate the effects of dietary DHA and EPA on gonadal steroidogenesis in mature females and males, with a feeding trial on tongue sole, a typical marine teleost with sexual dimorphism. Three experimental diets differing basically in DHA:EPA ratio, that is, 0·68 (diet D:E-0·68), 1·09 (D:E-1·09) and 2·05 (D:E-2·05), were randomly assigned to nine tanks of 3-year-old tongue sole (ten females and fifteen males in each tank). The feeding trail lasted for 90 d before and during the spawning season. Fish were reared in a flowing seawater system and fed to apparent satiation twice daily. Compared with diet D:E-0·68, diet D:E-1·09 significantly enhanced the oestradiol production in females, whereas diet D:E-2·05 significantly enhanced the testosterone production in males. In ovaries, diet D:E-1·09 induced highest mRNA expression of follicle-stimulating hormone receptor (FSHR), steroidogenic acute regulatory protein, 17α-hydroxylase (P450c17) and 3β-hydroxysteroid dehydrogenase (3β-HSD). In testes, diet 2·05 resulted in highest mRNA expression of FSHR, cholesterol side-chain cleavage enzyme, P450c17 and 3β-HSD. Fatty acid profiles in fish tissues reflected closely those of diets. Female fish had more gonadal EPA content but less DHA content than male fish, whereas there was a reverse observation in liver. In conclusion, the dietary DHA:EPA ratio, possibly combined with the dietary EPA:arachidonic acid ratio, differentially regulated sex steroid hormone synthesis in mature female and male tongue soles. Females seemed to require more EPA but less DHA for the gonadal steroidogenesis than males. The results are beneficial to sex-specific nutritive strategies in domestic teleost.

Liver phospholipids fatty acids composition in response to different types of diets in rats of both sexes

Background

Dietary intake influence changes in fatty acids (FA) profiles in liver which plays a central role in fatty acid metabolism, triacylglycerol synthesis and energy homeostasis. We investigated the effects of 4-weeks treatment with milk- and fish-based diet, on plasma biochemical parameters and FA composition of liver phospholipids (PL) in rats of both sexes.

Methods

Adult, 4 months old, Wistar rats of both sexes, were fed with different types of diets: standard, milk-based and fish-based, during 4 weeks. Analytical characterization of different foods was done. Biochemical parameters in plasma were determined. Fatty acid composition was analyzed by gas-chromatography. Statistical significance of FA levels was tested with two-way analysis of variance (ANOVA) using the sex of animals and treatment (type of diet) as factors on logarithmic or trigonometric transformed data.

Results

Our results showed that both, milk- and fish-based diet, changed the composition and ratio of rat liver phospholipids FA, in gender-specific manner. Initially present sex differences appear to be dietary modulated. Although, applied diets changed the ratio of total saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA), and effects were gender specific. Milk-based diet lowered SFA and elevated MUFA in males and increased PUFA in females vs. standard diet. The same diet decreased n-3, increased n-6 and n-6/n-3 ratio in males. Fish-based diet increased n-3, decreased n-6 and n-6/n-3 ratio vs. standard and milk-based diet in females. However, the ratio of individual FA in liver PL was also dietary-influenced, but with gender specific manner. While in females fish-based diet decreased AA (arachidonic acid) increased level of EPA (eicosapentaenoic acid), DPA (docosapentaenoic acid) and DHA (docosahexaenoic acid), the same diet elevated only DHA levels in males.

Conclusion

Gender related variations in FA composition of rat liver PL were observed, and results have shown that those initial differences could be significantly modulated by the type of diet. Furthermore, the modulatory effects of milk- and fish-based diets on liver phospholipids FA profiles appeared to be sex-specific.

Synergistic attenuation of ovariectomy-induced bone loss by combined use of fish oil and 17β-oestradiol

Oestrogen and n-3 PUFA, especially EPA and DHA, have been reported to have beneficial effects on bone loss. Thus, the purpose of the present study was to investigate the synergistic bone-protective mechanism of combined treatments of EPA+DHA supplementation and oestrogen injection in ovariectomised rats. Rats were fed a modified American Institute of Nutrition-93G diet with 0 %, 1 % or 2 % n-3 PUFA (EPA+DHA) relative to the total energy intake for 12 weeks. Rats were surgically ovariectomised at week 8, and after a 1-week recovery period rats were injected with either 17β-oestradiol-3-benzoate (E2) or maize oil for the last 3 weeks. Combined use of n-3 PUFA and E2 synergistically increased femoral cortical bone volume, bone mineral content and the bone expression of runt-related transcription factor 2 (RUNX2), but decreased the bone expression of IL-1β. Both n-3 PUFA and E2 decreased the bone expressions of IL-7, TNF-α and PPAR-γ, and increased the bone expression of oestrogen receptor-α. n-3 PUFA in the presence of E2 and E2 alone significantly decreased the bone expressions of IL-1β and IL-6 and increased the bone expression of RUNX2. E2 significantly decreased the serum levels of bone turnover markers and the bone expression of receptor activator of NF-κB ligand, but decreased the bone expression of osteoprotegerin. The combined use of n-3 PUFA and E2 exerted synergistic bone-protective efficacy through up-regulation of RUNX2, an essential transcription factor for bone formation, as well as the suppression of bone-resorbing cytokine IL-1β.

Serum Fatty Acids, Desaturase Activities and Abdominal Obesity - A Population-Based Study of 60-Year Old Men and Women

Abdominal obesity is a key contributor of metabolic disease. Recent trials suggest that dietary fat quality affects abdominal fat content, where palmitic acid and linoleic acid influence abdominal obesity differently, while effects of n-3 polyunsaturated fatty acids are less studied. Also, fatty acid desaturation may be altered in abdominal obesity. We aimed to investigate cross-sectional associations of serum fatty acids and desaturases with abdominal obesity prevalence in a population-based cohort study. Serum cholesteryl ester fatty acids composition was measured by gas chromatography in 60-year old men (n = 1883) and women (n = 2015). Cross-sectional associations of fatty acids with abdominal obesity prevalence and anthropometric measures (e.g., sagittal abdominal diameter) were evaluated in multivariable-adjusted logistic and linear regression models, respectively. Similar models were employed to investigate relations between desaturase activities (estimated by fatty acid ratios) and abdominal obesity. In logistic regression analyses, palmitic acid, stearoyl-CoA-desaturase and Δ6-desaturase indices were associated with abdominal obesity; multivariable-adjusted odds ratios (95% confidence intervals) for highest versus lowest quartiles were 1.45 (1.19–1.76), 4.06 (3.27–5.05), and 3.07 (2.51–3.75), respectively. Linoleic acid, α-linolenic acid, docohexaenoic acid, and Δ5-desaturase were inversely associated with abdominal obesity; multivariable-adjusted odds ratios (95% confidence intervals): 0.39 (0.32–0.48), 0.74 (0.61–0.89), 0.76 (0.62–0.93), and 0.40 (0.33–0.49), respectively. Eicosapentaenoic acid was not associated with abdominal obesity. Similar results were obtained from linear regression models evaluating associations with different anthropometric measures. Sex-specific and linear associations were mainly observed for n3-polyunsaturated fatty acids, while associations of the other exposures were generally non-linear and similar across sexes. In accordance with findings from short-term trials, abdominal obesity was more common among individuals with relatively high proportions of palmitic acid, whilst the contrary was true for linoleic acid. Further trials should examine the potential role of linoleic acid and its main dietary source, vegetable oils, in abdominal obesity prevention.

Effect of high carbohydrate diet on elongase and desaturase activity and accompanying gene expression in rat's liver

Background

Hepatic fatty acids (FAs) are modified through different metabolic pathways including elongation and desaturation. These processes are catalyzed by elongases and desaturases, respectively. Glucose, by transcription factors, regulates these processes. The aim of the study was to evaluate the influence of high carbohydrate diet (68%) on the expression of elongase (Elovl-2, Elovl-5, and Elovl-6) and desaturase (∆5D, ∆6D, Scd 1, Scd 2) genes and the activity of the enzymes. The changes in serum lipid profile (triglycerides (TG), total cholesterol (TC), HDL cholesterol) and glucose concentration were measured. Male Wistar rats were randomized into two study groups: animals fed with high carbohydrate diet (n = 6; HiCHO) and a control group fed with a standard diet (n = 6; ST). The expression of mRNA was determinate using reverse transcription PCR (RT-PCR). Hepatic FA composition was determined by gas chromatography, and FA ratios were used to estimate the activity of enzymes. Serum lipid profile and glucose concentration were measured using spectrophotometric methods.

Results

The mean values of transcript expression of all examined elongases and desaturases in liver HiCHO rats were higher as compared to ST. Higher expression did not always correspond to higher activity (as index). More monounsaturated FAs (MUFAs) were detected in the liver of HiCHO rats as compared to ST. Serum TG level was higher in the HiCHO than in ST.

Conclusions

These studies support the notion that the regulation of both Elovl and desaturase expression may play an important role in managing hepatic lipid composition in response to changes in dietary status.

The influence of sex and gonadectomy on hepatic and brain fatty acid composition, lipogenesis and β-oxidation

The aim of this study was to investigate the influence of sex and castration of rats on liver and brain fatty acid profile and liver mRNA expression of genes involved in lipogenesis and β-oxidation. Castration significantly increased body weight and liver index and decreased serum triglyceride content in the female rats. The fatty acid composition of the liver tissue was influenced by sex and castration. Male rats had higher content of C16:0, C18:1n7, C18:2n6 and C22:5n3, while female rats had higher content of C18:0, C20:4n6 and C22:6n3. Castration of male rats decreased differences caused by sex for C18:2n6, C20:4n6 and C22:6n3. Values for C16:1n7 were higher in the castrated male rats in comparison with all other groups. Liver phospholipids showed a distribution of fatty acids similar to the total lipids. Brain total lipids and phospholipids were not influenced by sex or castration. Castration increased ∆6D gene expression in both the sexes, while ∆5D and ∆9D increased in females and males respectively. Gonadectomy increased expression of the FASN gene in the females and decreased CPT1 and ACOX1 gene expression in the liver tissue of male rats. The observed results of lipid peroxidation, measured by TBARS, were the lowest in the intact females in comparison with all other groups. In conclusion, sex strongly influences both SFA and PUFA in liver tissue, and castration decreases these differences only for PUFA. Castration also influences the expression of the genes involved in lipid metabolism differently in male and female rats, with an increase in lipogenic genes in female rats and a decrease in key genes for mitochondrial and peroxisomal β-oxidation in male rats.

Differences in long chain polyunsaturates composition and metabolism in male and female rats

Human studies and some animal work have shown more docosahexaenoic acid (DHA) and arachidonic acid (ARA) was accumulated or converted from precursors in females compared to males. This study explored in-depth the effect of gender on fatty acid composition and polyunsaturated fatty acid metabolism in rats fed one of two well-defined diets containing 10% total fat. One diet contained 15% of linoleic acid (LA) and 3% of α-linolenic acid (ALA) of the total fatty acids (LA+ALA diet), while the other diet contained 15% LA and 0.05% ALA (LA diet). At the age of 20 weeks, all animals were orally administered a single dose of a mixture of deuterium-labeled LA and ALA. Caudal venous blood was then drawn at 0, 2, 4, 8, 12, 24, 48, 96 and 168h. The concentrations of the deuterated precursors and their metabolites in plasma total lipids were quantified by GC/MS negative chemical ionization. Endogenous fatty acids were quantified by GC/FID analysis. When expressed as the percentage of oral dosage, female rats accumulated more precursors and more products, deuterated DHA and deuterated n-6 docosapentaenoic acid (²H₅-DPAn-6), in plasma than did male rats in both the LA+ALA diet and the LA diet. For the endogenous non-labeled PUFA, greater concentrations of DHA and DPAn-6 were similarly observed in female rats compared to males within each diet. A lower concentration of non-labeled ARA was observed only in female rats fed the LA+ALA diet. In summary, greater endogenous and exogenous DHA and DPAn-6 was observed in female rat plasma and this was independent of dietary ALA status.

Sexually dimorphic brain fatty acid composition in low and high fat diet-fed mice

OBJECTIVE

In this study, we analyzed the fatty acid profile of brains and plasma from male and female mice fed chow or a western-style high fat diet (WD) for 16 weeks to determine if males and females process fatty acids differently. Based on the differences in fatty acids observed in vivo, we performed in vitro experiments on N43 hypothalamic neuronal cells to begin to elucidate how the fatty acid milieu may impact brain inflammation.

METHODS

Using a comprehensive mass spectrometry fatty acid analysis, which includes a profile for 52 different fatty acid isomers, we assayed the plasma and brain fatty acid composition of age-matched male and female mice maintained on chow or a WD. Additionally, using the same techniques, we determined the fatty acid composition of N43 hypothalamic cells following exposure to palmitic and linoleic acid, alone or in combination.

RESULTS

Our data demonstrate there is a sexual dimorphism in brain fatty acid content both following the consumption of the chow diet, as well as the WD, with males having an increased percentage of saturated fatty acids and reductions in ω6-polyunsaturated fatty acids when compared to females. Interestingly, we did not observe a sexual dimorphism in fatty acid content in the plasma of the same mice. Furthermore, exposure of N43 cells to the ω6-PUFA linoleic acid, which is higher in female brains when compared to males, reduces palmitic acid-induced inflammation.

CONCLUSIONS

Our data suggest male and female brains, and not plasma, differ in their fatty acid profile. This is the first time, to our knowledge, lipidomic analyses has been used to directly test the hypothesis there is a sexual dimorphism in brain and plasma fatty acid composition following consumption of the chow diet, as well as following exposure to the WD.

Prevention of hyperphagia prevents ovariectomy-induced triacylglycerol accumulation in liver, but not plasma

Menopause is associated with higher plasma and liver triacylglycerol (TAG) and increased risk for cardiovascular disease. Lowering TAG in menopause may be beneficial; however, the mechanism underlying menopause-induced TAG accumulation is not clear. Ovariectomy is a model for menopause and is associated with metabolic alterations and hyperphagia. This study investigated the role of hyperphagia in ovariectomy-induced increases in blood and tissue TAG, as well as differences in lipid metabolism enzymes and resting metabolic measures. It was hypothesized that prevention of hyperphagia would restore blood and tissue TAG, enzyme expression, and metabolic measures to eugonadal levels. Ovariectomized rats were fed ad libitum (OVX + AL) or pair-fed (OVX + PF) relative to sham-operated rats (SHAM) to prevent hyperphagia. OVX + AL had higher TAG concentrations in liver and plasma than SHAM (60% and 50%, respectively), and prevention of hyperphagia in OVX + PF normalized TAG concentrations to SHAM levels in liver, but not plasma. OVX + AL also had 141% higher hepatic stearoyl-CoA desaturase 1 which was almost completely normalized to SHAM levels by pair-feeding, suggesting normalization of hepatic lipid storage. In contrast, skeletal muscle carnitine palmitoyl transferase 1 was 40% lower in OVX + AL than SHAM and was intermediate in OVX + PF, suggesting lower muscle fatty acid oxidation that may underlie the higher plasma TAG in OVX. No differences were seen in energy expenditure, VO2, or VCO2. Overall, this study indicates that prevention of hyperphagia resulting from ovarian hormone withdrawal normalizes hepatic TAG to eugonadal levels but has no effect on ovariectomy-induced increases in plasma TAG.

Synergic hypocholesterolaemic effect of n-3 PUFA and oestrogen by modulation of hepatic cholesterol metabolism in female rats

n-3 PUFA such as EPA and DHA as well as oestrogen have been reported to decrease blood levels of cholesterol, but their underlying mechanism is unclear. The purpose of this study was to determine the effects of the combination of n-3 PUFA supplementation and oestrogen injection on hepatic cholesterol metabolism. Rats were fed a modified AIN-93G diet with 0, 1 or 2 % n-3 PUFA (EPA+DHA) relative to the total energy intake for 12 weeks. Rats were surgically ovariectomised at week 8, and, after 1-week recovery, rats were injected with 17β-oestradiol-3-benzoate (E2) or maize oil for the last 3 weeks. Supplementation with n-3 PUFA and E2 injection significantly increased the ratio of the hepatic expression of phosphorylated AMP activated protein kinase (p-AMPK):AMP activated protein kinase (AMPK) and decreased sterol regulatory element-binding protein-2, 3-hydroxy-3-methylglutaryl coenzyme A reductase and proprotein convertase subtilisin/kexin type 9. Supplementation with n-3 PUFA increased hepatic expression of cholesterol 7α-hydroxylase (CYP7A1), sterol 12α-hydroxylase (CYP8B1) and sterol 27-hydroxylase (CYP27A1); however, E2 injection decreased CYP7A1 and CYP8B1 but not CYP27A1. Additionally, E2 injection increased hepatic expression of oestrogen receptor-α and β. In conclusion, n-3 PUFA supplementation and E2 injection had synergic hypocholesterolaemic effects by down-regulating hepatic cholesterol synthesis (n-3 PUFA and oestrogen) and up-regulating bile acid synthesis (n-3 PUFA) in ovariectomised rats.

Fasting enriches liver triacylglycerol with n-3 polyunsaturated fatty acids: implications for understanding the adipose-liver axis in serum docosahexaenoic acid regulation

We investigated the effect of short-term fasting on coordinate changes in the fatty acid composition of adipose triacylglycerol (TAG), serum non-esterified fatty acids (NEFA), liver TAG, and serum TAG and phospholipids in mice fed ad libitum or fasted for 16 h overnight. In contrast to previous reports under conditions of maximal lipolysis, adipose tissue TAG was not preferentially depleted of n-3 PUFA or any specific fatty acids, nor were there any striking changes in the serum NEFA composition. Short-term fasting did, however, increase the hepatic proportion of n-3 PUFA, and almost all individual species of n-3 PUFA showed relative and absolute increases. The relative proportion of n-6 PUFA in liver TAG also increased but to a lesser extent, resulting in a significant decrease in the n-6:n-3 PUFA ratio (from 14.3 ± 2.54 to 9.6 ± 1.20), while the proportion of MUFA decreased significantly and SFA proportion did not change. Examination of genes involved in PUFA synthesis suggested that hepatic changes in the elongation and desaturation of precursor lipids could not explain this effect. Rather, an increase in the expression of fatty acid transporters specific for 22:6n-3 and other long-chain n-3 and n-6 PUFA likely mediated the observed hepatic enrichment. Analysis of serum phospholipids indicated a specific increase in the concentration of 22:6n-3 and 16:0, suggesting increased specific synthesis of DHA-enriched phospholipid by the liver for recirculation. Given the importance of blood phospholipid in distributing DHA to neural tissue, these findings have implications for understanding the adipose-liver-brain axis in n-3 PUFA metabolism.

Estrogen and n-3 polyunsaturated fatty acid supplementation have a synergistic hypotriglyceridemic effect in ovariectomized rats

The n-3 polyunsaturated fatty acids (PUFAs), EPA and DHA, as well as estrogen have been shown to decrease circulating levels of triglyceride (TG), but their underlying mode of action is unclear. The purpose of this study was to determine the effects of n-3 PUFA consumption and estrogen injection on TG metabolism. Rats (n = 48) were fed a modified AIN-93G diet with 0, 1, or 2 % EPA + DHA relative to the total energy intake during 12 weeks. At 8 weeks, rats were ovariectomized (OVX), and after a 1-week recovery, rats were injected with either 17β-estradiol-3-benzoate (E2) or corn oil for the last 3 weeks. The n-3 PUFA consumption and E2 injection independently decreased the hepatic expressions of sterol regulatory element-binding protein 1, acetyl-CoA carboxylase 1, fatty acid synthase (FAS), and diacylglycerol acyltransferase 2 (DGAT2) (P < 0.05). There were interactions between n-3 PUFA consumption and E2 injection on hepatic expression of FAS and DGAT2. In addition, n-3 PUFA consumption and E2 injection up-regulated the expression of AMP-activated protein kinase (AMPK), phosphorylated AMPK, peroxisomal proliferator-activated receptor α, and carnitine palmitoyltransferase 1 in liver and skeletal muscle. E2 injection increased the expression of estrogen receptor α and β in skeletal muscle and liver, but n-3 PUFA consumption increased the expression of both receptors only in skeletal muscle. The present study suggests that the hypotriglyceridemic effects of n-3 PUFA consumption and E2 injection could be due to the down-regulation of hepatic TG synthesis and up-regulation of TG oxidation in liver and skeletal muscle in OVX rats.

Inducing effect of clofibric acid on stearoyl-CoA desaturase in intestinal mucosa of rats

Fibrates have been reported to elevate the hepatic proportion of oleic acid (18:1n-9) through inducing stearoyl-CoA desaturase (SCD). Despite abundant studies on the regulation of SCD in the liver, little is known about this issue in the small intestine. The present study aimed to investigate the effect of clofibric acid on the fatty acid profile, particularly monounsaturated fatty acids (MUFA), and the SCD expression in intestinal mucosa. Treatment of rats with a diet containing 0.5% (w/w) clofibric acid for 7 days changed the MUFA profile of total lipids in intestinal mucosa; the proportion of 18:1n-9 was significantly increased, whereas those of palmitoleic (16:1n-7) and cis-vaccenic (18:1n-7) acids were not changed. Upon the treatment with clofibric acid, SCD was induced and the gene expression of SCD1, SCD2, and fatty acid elongase (Elovl) 6 was up-regulated, but that of Elovl5 was unaffected. Fat-free diet feeding for 28 days increased the proportions of 16:1n-7 and 18:1n-7, but did not effectively change that of 18:1n-9, in intestinal mucosa. Fat-free diet feeding up-regulated the gene expression of SCD1, but not that of SCD2, Elovl6, or Elovl5. These results indicate that intestinal mucosa significantly changes its MUFA profile in response to challenges by clofibric acid and a fat-free diet and suggest that up-regulation of the gene expression of SCD along with Elovl6 is indispensable to elevate the proportion of 18:1n-9 in intestinal mucosa.

Aqueous extract of post-fermented tea reverts the hepatic steatosis of hyperlipidemia rat by regulating the lipogenic genes expression and hepatic fatty acid composition

BACKGROUND

Post-fermented tea has been used for the prevention of metabolic syndrome in Western China. Present study reports the biochemical mechanism of lipid-lowering effects of Jing-wei fu tea (JWFT), a variety of post-fermented tea on high-fat diet-induced hyperglycemia and obesity in rats.

METHODS

Aqueous extract of JWFT was prepared by putting them in boiling water, and then concentrated under reduced pressure. The major compounds of JWFT were determined by high performance liquid chromatography (HPLC). High-fat diet fed rats were orally administered different doses of JWFT aqueous extract (0.5, 1.0 and 2.0 g/kg) for four weeks. At the end of this experiment, hepatic lipids, serum leptin and lipids levels were determined using enzyme-linked immunosorbent assay (ELISA). The hepatic fatty acid composition was analyzed using gas chromatography mass (GC-MS). The relative expression of lipids metabolism genes was analyzed using reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

The results showed that JWFT inhibited the increase in the body weight, abdominal adipose weight, serum lipids and hepatic lipids, and decreased serum leptin levels of high-fat diet fed rats. JWFT normalized hepatic fatty acid composition of hyperlipidemia rats by up-regulating hepatic acetyl-CoA carboxylase (ACC), stearoyl-CoA desaturase 1 (SCD1) and fatty acid synthase (FAS) gene expression, and down-regulating carnitine palmitoyl transferase-1 (CPT1). Furthermore, the results showed that JWFT inhibited the absorption of lipids.

CONCLUSION

JWFT could mitigate the obesity-induced hepatic steatosis by regulating hepatic lipogenesis and lipolysis.

Inhibition of stearoyl-CoA desaturase-1 in differentiating 3T3-L1 preadipocytes upregulates elongase 6 and downregulates genes affecting triacylglycerol synthesis

BACKGROUND

Stearoyl-CoA desaturase-1 (SCD1) is rate limiting for the conversion of saturated fatty acids palmitate (16:0) and stearate (18:0) to monounsaturated fatty acids palmitoleate (16:1n7) and oleate (18:1n9), respectively. Given that reduced SCD1 activity is associated with improved insulin sensitivity and decreased body weight, there is considerable interest to elucidate the role of this enzyme in adipocytes. During adipogenesis, SCD1 levels increase concomitantly with the accumulation of triacylglycerol (TG); however, the extent to which reduced SCD1 activity can influence TG synthesis and metabolic pathways in differentiating adipocytes remains relatively unexplored.

OBJECTIVE

The aim of this work was to delineate how reduced SCD1 activity affects gene expression, protein content and cellular fatty acids in differentiating murine preadipocytes.

METHODS

3T3-L1 preadipocytes were treated with an SCD1 inhibitor (10 nM) throughout differentiation. After 7 days, global gene expression, protein content and fatty acid profiles were examined using microarrays, western blotting and gas chromatography, respectively.

RESULTS

SCD1 inhibition increased the abundance of 16:0 and 18:0 (45% and 194%, respectively) and decreased 16:1n7 and 18:1n7 (61% and 35%, respectively) in differentiated preadipocytes. Interestingly, 18:1n9 levels increased by 61%. The augmented 18:0 suggested a possible increase in elongase activity. Elongase 6 (Elovl6) gene expression was increased 2.8-fold (P = 0.04); however, changes were not detected for ELOVL6 protein content. Microarray analysis revealed that genes affecting TG synthesis were downregulated with SCD1 inhibition, which coincided with a 33% decrease in cellular TG content.

CONCLUSION

These results provide new mechanistic insight into the role of SCD1 as a regulator of fatty acid profiles and TG synthesis in adipocytes, and reinforce that modulating SCD1 activity may help reduce the risk of obesity-related complications.

Effect of sex hormones on plasma phospholipid fatty acid composition in intact rats and rats with bilaterally occluded carotid arteries

The effects of 8-days treatment with 17alpha-estradiol (33.3 microg/kg) and progesterone (1.7 mg/kg) on plasma lipids and fatty acid composition of plasma phospholipids were examined in intact (INT) and bilaterally common carotid arteries occluded (BCO) male Wistar rats. Significant decrease of triglyceride level was found in BCO rats after the estradiol treatment. Both hormones elevated proportion of 18:1n-7 fatty acid in INT, but they failed to have such an effect in BCO. Estradiol increased 22:5n-3 and total n-3 polyunsaturated fatty acids (PUFA) in intact, and decreased 18:2n-6 in BCO rats. Significantly lower level of total n-3 was found in progesterone-treated than in estradiol-treated BCO rats. Given that n-3 PUFA have many beneficial effects on cell and tissue function, while n-6 PUFA have mostly the opposite effects, estradiol, rather than progesterone, was seen to improve plasma lipids and phospholipids FA profiles in INT and BCO animals. Estradiol significantly elevated the estimated activity of delta9-desaturases and progesterone of delta5-desaturase in BCO group, with no effects in INT rats.

Monounsaturated fatty acids generated via stearoyl CoA desaturase-1 are endogenous inhibitors of fatty acid amide hydrolase

High-fat diet (HFD)-induced obesity and insulin resistance are associated with increased activity of the endocannabinoid/CB1 receptor (CB1R) system that promotes the hepatic expression of lipogenic genes, including stearoyl-CoA desaturase-1 (SCD1). Mice deficient in CB1R or SCD1 remain lean and insulin-sensitive on an HFD, suggesting a functional link between the two systems. The HFD-induced increase in the hepatic levels of the endocannabinoid anandamide [i.e., arachidonoylethanolamide (AEA)] has been attributed to reduced activity of the AEA-degrading enzyme fatty acid amide hydrolase (FAAH). Here we show that HFD-induced increased hepatic AEA levels and decreased FAAH activity are absent in SCD1(-/-) mice, and the monounsaturated fatty acid (MUFA) products of SCD1, palmitoleic and oleic acid, inhibit FAAH activity in vitro at low micromolar concentrations. HFD markedly increases hepatic SCD1 activity in WT mice as well as in CB1R(-/-) mice with transgenic reexpression of CB1R in hepatocytes, but not in global CB1R(-/-) mice. Treatment of HFD-fed mice with the SCD1 inhibitor A939572 prevents the diet-induced reduction of hepatic FAAH activity, normalizes hepatic AEA levels, and improves insulin sensitivity. SCD1(-/-) mice on an HFD remain insulin-sensitive, but develop glucose intolerance and insulin resistance in response to chronic treatment with the FAAH inhibitor URB597. An HFD rich in MUFA or feeding mice pure oleic acid fail to inhibit hepatic FAAH activity. We conclude that MUFAs generated via SCD1 activity, but not diet-derived MUFAs, function as endogenous FAAH inhibitors mediating the HFD-induced increase in hepatic AEA, which then activates hepatic CB1R to induce insulin resistance.

Stearoyl-CoA desaturase 1, elongase 6 and their fatty acid products and precursors are altered in ovariectomized rats with 17β-estradiol and progesterone treatment

Sex differences in monounsaturated fatty acid (MUFA) levels suggest ovarian hormones may affect MUFA biosynthesis. Sprague-Dawley rats (8 weeks of age) were ovariectomized or sham operated with ovariectomized rats implanted with a constant-release hormone pellet providing 17β-estradiol, progesterone, both or neither at 10 weeks of age. After 14 days, rats were fasted overnight and sacrificed to collect plasma and livers for analysis. Hepatic stearoyl-CoA desaturase (SCD1) expression was unchanged between ovariectomized and sham controls, as determined by microarray and immunoblotting. However, SCD1 protein was increased in rats treated with estradiol plus progesterone. Elongase 6 protein levels were increased with 17β-estradiol treatment compared with sham. Rats treated with 17β-estradiol and 17β-estradiol plus progesterone had increased 16:0, 18:0, 16:1n-7 and 18:1n-7 in hepatic and plasma phospholipids. Ovarian hormones appear to be involved with MUFA biosynthesis, but the relationship appears complex and involves elongase 6 and SCD1.