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1.
Aims/hypothesis The aim of this study was to investigate whether lifestyle intervention-induced changes in serum fatty acid profile of cholesteryl
esters and estimated desaturase activities are related to improvements in insulin sensitivity in subjects at risk of type
2 diabetes.
Materials and methods In the Study on Lifestyle Intervention and Impaired Glucose Tolerance Maastricht (SLIM), 97 men and women with IGT were randomised
to a combined diet and exercise programme (47 intervention) or a control group (50 control subjects). At baseline and after
1 year the following assessments were made: an OGTT, an exercise test to determine maximal aerobic capacity, anthropometry,
and analysis of the serum fatty acid profile of cholesteryl esters.
Results The lifestyle programme was effective in reducing the intake of total and saturated fat, increasing physical activity, reducing
obesity and improving insulin sensitivity and glucose tolerance. Regression analysis of the total population showed that an
increase in the C20:4 n-6/C20:3 n-6 ratio (estimated Δ5-desaturase activity) and reductions in the C18:3 n-6/C18:2 n-6 ratio (estimated Δ6-desaturase activity) and the C16:1 n-7/C16:0 ratio (estimated Δ9-desaturase activity or stearoyl-CoA desaturase-1) were significantly associated with a decrease
in homeostasis model assessment for insulin resistance. After adjustment for lifestyle changes (change in percentage body
fat, aerobic capacity and saturated fat intake), these associations were partly reduced, but remained statistically significant.
Conclusions/interpretation Lifestyle-induced changes in fatty acid profile of cholesteryl esters and desaturase activities were independently related
to changes in insulin sensitivity in subjects at risk of type 2 diabetes. 相似文献
2.
Aims/hypothesis Previous studies have shown relationships between fatty acid ratios in adipose tissue triacylglycerol (TG), adipocyte size
and measures of insulin sensitivity. We hypothesised that variations in adipose tissue de novo lipogenesis (DNL) in relation
to adiposity might explain some of these observations.
Methods In a cross-sectional study, subcutaneous abdominal adipose tissue biopsies from 59 people were examined in relation to fasting
and post-glucose insulin sensitivity. Adipocyte size, TG fatty acid composition and mRNA expression of lipogenic genes were
determined.
Results We found strong positive relationships between adipose tissue TG content of the fatty acids myristic acid (14:0) and stearic
acid (18:0) with insulin sensitivity (HOMA model) ( p < 0.01 for each), and inverse relationships with adipocyte size ( p < 0.01, p < 0.05, respectively). Variation in 18:0 content was the determinant of the adipose tissue TG 18:1 n-9/18:0 ratio, which correlated negatively with insulin sensitivity ( p < 0.01), as observed previously. Adipose tissue 18:0 content correlated positively with the mRNA expression of lipogenic
genes (e.g. FASN, p < 0.01). Lipogenic gene expression (a composite measure derived from principal components analysis) was inversely correlated
with adipocyte cell size ( p < 0.001). There was no relationship between dietary saturated fatty acid intake and adipose tissue 18:0 content.
Conclusions/interpretation Our data suggest a physiological mechanism whereby DNL is downregulated as adipocytes expand. Taken together with other data,
they also suggest that hepatic and adipose tissue DNL are not regulated in parallel. We also confirm a strong relationship
between small adipocytes and insulin sensitivity, which is independent of BMI.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users. 相似文献
3.
Aims/hypothesis Stearoyl-CoA desaturase 1 (SCD1) is the rate-limiting enzyme in monounsaturated fatty acid synthesis. It is imperative for
the assembly of VLDL particles, which transport triacylglycerol (TG) from liver to adipose tissue and other sites. We aimed
to determine the role of hepatic SCD1 activity in human glucose and lipid metabolism.
Methods We studied 54 people participating in a lifestyle intervention programme with diet modification and increased physical activity.
Insulin sensitivity was determined during a euglycaemic–hyperinsulinaemic clamp and estimated from an OGTT. Liver fat was
quantified by 1H-magnetic resonance spectroscopy at baseline and after 9 months of intervention. The pattern of fatty acids in serum VLDL-TGs
was determined by ultracentrifugation followed by thin layer and gas chromatography, with the 18:1 n-9: 18:0 ratio providing an index of hepatic SCD1 activity.
Results The hepatic SCD1 activity index correlated negatively with liver fat ( r = −0.29, p = 0.04) and positively with insulin sensitivity, both OGTT-derived ( r = 0.42, p = 0.003) and clamp-derived ( r = 0.27, p = 0.07). These correlations depended on overall adiposity. They were absent in leaner participants ( n = 27, liver fat: p = 0.34, insulin sensitivity [OGTT]: p = 0.75, insulin sensitivity [clamp]: p = 0.24), but were strong in obese individuals ( n = 27, p = 0.004, p = 0.0002 and p = 0.006, respectively). Furthermore, during intervention a high SCD1 activity index at baseline predicted a decrease in liver
fat only in obese participants ( r = −0.46, p = 0.02).
Conclusions/interpretation Our data suggest that high hepatic SCD1 activity may regulate fat accumulation in the liver and possibly protects from insulin
resistance in obesity.
N. Stefan and A. Peter contributed equally to this work. 相似文献
4.
Objective:Subcutaneous (SC) adipose tissue stearic acid (18:0) content and stearoyl-CoA desaturase-1 (SCD1)-mediated production of oleic acid (18:1) have been suggested to be altered in obesity. The objective of our study was to examine abdominal adipose tissue fatty acid content and SCD1 mRNA/protein level in women. Subjects and methods:Fatty acid content was determined by capillary gas chromatography in SC and omental (OM) fat tissues from two subgroups of 10 women with either small or large OM adipocytes. Samples from 10 additional women were used to measure SCD1 mRNA and protein expression, total extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphorylated ERK1/2 protein as well as insulin receptor (IR) expression levels. Results:OM fat 18:0 content was significantly lower in women with large OM adipocytes compared with women who had similar adiposity, but small OM adipocytes (2.37±0.45 vs 2.75±0.30 mg per 100 g adipose tissue, respectively, P⩽0.05). OM fat 18:0 content was negatively related to the visceral adipose tissue area ( r=−0.44, P=0.05) and serum triglyceride levels ( r=−0.56, P<0.05), while SC fat 18:0 content was negatively correlated with total body fat mass (BFM) ( r=−0.48, P<0.05) and fasting insulin concentration ( r=−0.73, P<0.005). SC adipose tissue desaturation index (18:1/18:0), SCD1 expression and protein levels were positively correlated with BFM. Moreover, obese women were characterized by a reduced OM/SC ratio of SCD1 mRNA and protein levels. A similar pattern was observed for ERK1/2 and IR expression. Conclusion:The presence of large adipocytes and increased adipose mass in a given fat compartment is related to reduced 18:0 content and increased desaturation index in women, independently of dietary fat intake. The depot-specific difference in ERK1/2 expression and activation, as well as in SCD1 and IR expression in obese women is consistent with the hypothesis that they may predominantly develop SC fat, which could in turn help protect from metabolic disorders. 相似文献
5.
Aims/hypothesis Types of dietary fat have been related to components of the metabolic syndrome. Serum fatty acid composition mainly reflects dietary fat intake, but also endogenous fatty acid synthesis catalysed by -desaturases. It is not known whether alterations of fatty acid composition or desaturase activities predict metabolic syndrome.Materials and methods We prospectively evaluated fatty acid composition in serum cholesteryl esters and estimated desaturase activities in 1,558 50-year-old men taking part in a population-based cohort study. The follow-up time was 20 years. Stearoyl-CoA desaturase (SCD-1), 6 (D6D) and 5 (D5D) desaturases were estimated as precursor to fatty acid ratios.Results High activity of estimated SCD-1 (odds ratio=1.29, p<0.05) and D6D (odds ratio=1.35, p<0.05), as well as low estimated D5D activity (odds ratio=0.71, p<0.001) predicted the development of metabolic syndrome (as defined by the National Cholesterol Education Program). The predictive value of D5D activity was independent of lifestyle factors (smoking, BMI and physical activity), whereas the risk associated with higher SCD-1 and D6D activities was mainly explained by obesity. Among those developing metabolic syndrome (119 out of 706) during follow-up, the proportions of fatty acids 14:0, 16:0, 16:1 ( n–7), 18:1 ( n–9), 18:3 ( n–6) and 20:3 ( n–6) were increased at baseline, while 18:2 ( n–6) was decreased ( p<0.05 for all).Conclusions/interpretation Serum fatty acid composition predicts the long-term development of the metabolic syndrome, and D5D activity may be particularly important in this process. Our results suggest a role of dietary fat quality in the development of metabolic syndrome, but the possibility that altered fatty acid composition, partly secondary to genetic or hormonal factors, should also be considered. 相似文献
6.
Aim: Kinin B 1 receptor (B 1R) contributes to insulin resistance through a mechanism involving oxidative stress. This study examined the effect of B 1R blockade on the changes in plasma fatty acids composition, body and tissue fat mass and adipose tissue inflammation that influence insulin resistance. Methods: Sprague–Dawley rats were fed with 10% D‐glucose or tap water (Control) for 13 weeks and during the last week, rats were administered the B 1R antagonist SSR240612 (10 mg/kg/day, gavage) or vehicle. The following parameters were assessed: plasma fatty acids (by gas chromatography), body composition (by EchoMRI), metabolic hormone levels (by radioimmunoassay), expression of B 1R and inflammatory markers in adipose tissue (by Western blot and qRT‐PCR). Results: Glucose feeding significantly increased plasma levels of glucose, insulin, leptin, palmitoleic acid (16:1n‐7), oleic acid (18:1n‐9), Δ6 and Δ9 desaturases while linoleic acid (18:2n‐6), arachidonic acid (20:4n‐6) and Δ5 desaturase were decreased. SSR240612 reduced plasma levels of insulin, glucose, the homeostasis model assessment index of insulin resistance, palmitoleic acid and n‐7 family. Alterations of Δ5, Δ6 and Δ9 desaturases were normalized by SSR240612. The B 1R antagonist also reversed the enhancing effect of glucose feeding on whole body and epididymal fat mass and on the expression of macrophage CD68, interleukin‐1 β, tumour necrosis factor‐ α and inducible nitric oxide synthase in retroperitoneal adipose tissue. B 1R protein and mRNA were not detected in retroperitoneal adipose tissue. Conclusion: Insulin resistance in glucose‐fed rats is associated with low state inflammation in adipose tissue and plasma fatty acids changes which are reversed by B 1R blockade. These beneficial effects may contribute to insulin sensitivity improvement and the prevention of obesity. 相似文献
7.
Linoleic acid (18:2n-6) and alpha-linolenic acid (18:3n-3) are polyunsaturated fatty acids that are essential for mammalian nutrition, because mammals lack the desaturases required for synthesis of Delta12 (n-6) and n-3 fatty acids. Many plants can synthesize these fatty acids and, therefore, to examine the effects of a plant desaturase in mammals, we generated transgenic pigs that carried the fatty acid desaturation 2 gene for a Delta12 fatty acid desaturase from spinach. Levels of linoleic acid (18:2n-6) in adipocytes that had differentiated in vitro from cells derived from the transgenic pigs were approximately 10 times higher than those from wild-type pigs. In addition, the white adipose tissue of transgenic pigs contained approximately 20% more linoleic acid (18:2n-6) than that of wild-type pigs. These results demonstrate the functional expression of a plant gene for a fatty acid desaturase in mammals, opening up the possibility of modifying the fatty acid composition of products from domestic animals by transgenic technology, using plant genes for fatty acid desaturases. 相似文献
8.
Background and aimsDirect measurement of desaturase activities are difficult to obtain in humans. Consequently, surrogate measures of desaturase activity (estimated desaturase activities) have been frequently used in observational studies, and estimated Δ 9- (or stearoyl-CoA-desaturase (SCD)), Δ 6- and Δ 5-desaturase activities have been associated with cardiometabolic disease. Data on how the markers of desaturase activities are modified by changes in dietary fat quality are lacking and therefore warrant examination. Methods and resultsIn a two-period (three weeks) strictly controlled cross-over study, 20 subjects (six women and 14 men) consumed a diet high in saturated fat (SAT-diet) and a rapeseed oil diet (RO-diet), rich in oleic acid (OA), linoleic acid (LA) and α-linolenic acid (ALA). Estimated desaturase activities were calculated as precursor to product FA ratios in serum cholesteryl esters and phospholipids. The estimated SCD [16:1 n-7/16:0] and Δ 6-desaturase [20:3 n-6/18:2 n-6] was significantly higher while Δ 5-desaturase [20:4 n-6/20:3 n-6] was significantly lower in the SAT-diet ( P < 0.001 for all), compared to the RO-diet. The serum proportions of palmitic, stearic, palmitoleic and dihomo-γ-linolenic acids were significantly higher in the SAT-diet while the proportions of LA and ALA were significantly higher in the RO-diet. ConclusionThis is the first study to demonstrate that surrogate measures of desaturase activities change as a consequence of an alteration in dietary fat quality. Both the [16:1/16:0]-ratio and 16:1 seem to reflect changes in saturated fat intake and may be useful markers of saturated fat intake in Western countries. 相似文献
9.
Long-lived individuals (LLIs) are considered an ideal model to study healthy human aging. Blood fatty acid (FA) profile of a cohort of LLIs (90–111 years old, n?=?49) from Sicily was compared to adults (18–64 years old, n?=?69) and older adults (65–89 years old, n?=?54) from the same area. Genetic variants in key enzymes related to FA biosynthesis and metabolism were also genotyped to investigate a potential genetic predisposition in determining the FA profile. Gas chromatography was employed to determine the FA profile, and genotyping was performed using high-resolution melt (HRM) analysis. Blood levels of total polyunsaturated FA (PUFA) and total trans-FA decreased with age, while the levels of saturated FA (SFA) remained unchanged. Interestingly, distinctively higher circulatory levels of monounsaturated FA (MUFA) in LLIs compared to adults and older adults were observed. In addition, among LLIs, rs174537 in the FA desaturase 1/2 (FADS1/2) gene was associated with linoleic acid (LA, 18:2n-6) and docosatetraenoic acid (DTA, 22:4n-6) levels, and the rs953413 in the elongase of very long FA 2 (ELOVL2) was associated with DTA levels. We further observed that rs174579 and rs174626 genotypes in FADS1/2 significantly affect delta-6 desaturase (D6D) activity. In conclusion, our results suggest that the LLIs have a different FA profile characterized by high MUFA content, which indicates reduced peroxidation while maintaining membrane fluidity. 相似文献
10.
Background and aimAltered fatty acid patterns in blood may be associated with insulin resistance and related disorders. We investigated whether serum proportions of cholesteryl fatty acids and desaturase activity are associated with glucose tolerance status and insulin resistance. Methods and resultsData were obtained from a cross-sectional study among 471 Dutch participants aged ≥40 years. Individual fatty acids in serum cholesteryl esters were determined and endogenous conversions by desaturases were estimated from product-to-precursor ratios. Proportions of fatty acids were compared among participants with normal glucose tolerance, impaired glucose metabolism and newly diagnosed type 2 diabetes. Partial Spearman correlation coefficients between fatty acids and homeostasis model assessment-insulin resistance (HOMA-IR) were calculated. Adjustments were made for lifestyle and nutritional factors.The proportions of total saturated, mono-unsaturated, trans- and poly-unsaturated fatty acids did not differ significantly between groups, but several individual fatty acids did; the proportions of C18:0 and C20:3 n6 were higher, whereas those of C18:1 n7 and C20:4 n6 were lower in participants with type 2 diabetes compared with those with normal glucose tolerance. Activity of Δ5-desaturase, that is, ratio of C20:4 n6 to C20:3 n6, was lower ( p < 0.01) in participants with type 2 diabetes (7.4) than with normal glucose tolerance (8.4). HOMA-IR was correlated positively with Δ9-desaturase activity ( r = 0.11, p < 0.01) and inversely with Δ5-desaturase activity ( r = ?0.21, p < 0.01). ConclusionThe observed lower Δ5-desaturase activity in participants with type 2 diabetes and its inverse association with HOMA-IR suggest that changes in fatty-acid metabolism may play a role in the aetiology of type 2 diabetes. 相似文献
11.
Aims/hypothesis Stearoyl-CoA desaturase (SCD) is emerging as a key regulator of lipid and carbohydrate metabolism. Scd-null mice display a beneficial metabolic phenotype characterised by resistance to obesity, diabetes and hyperlipidaemia. The human homologue, SCD, maps to a region of chromosome 10 linked to type 2 diabetes, and SCD activity correlates with insulin sensitivity. Given this strong positional and biological candidacy, the present study sought to establish whether sequence variation in SCD influences susceptibility to type 2 diabetes and related traits.Methods The SCD gene was resequenced in 23 diabetic subjects. Six variants within coding and adjacent sequence, including a non-synonymous SNP in exon 5 (M224L), were selected for genotyping in a primary set of 608 diabetic subjects and 600 control subjects.Results There was no association (at the allele, genotype or haplotype level) with type 2 diabetes, although genotype frequencies at the +14301 A>C SNP in the 3 untranslated region showed borderline association ( p~0.06) when evidence for linkage was taken into account. However, replication studies (350 young-onset diabetic patients; 747 controls) failed to confirm any relationship with diabetes for this variant. No significant associations were seen for diabetes-related traits including BMI and waist-to-hip ratio.Conclusions/interpretation The present study, the first reported analysis of this gene, indicates that the SCD variants typed do not explain chromosome-10-encoded susceptibility to type 2 diabetes. Although this study provided no evidence that SCD sequence variation influences diabetes susceptibility or related traits, SCD remains a major target for pharmaceutical and/or environmental manipulation. 相似文献
12.
Summary Numerous studies show an association between poor fetal growth and adult insulin resistance. Recent studies have shown relation
between the long chain polyunsaturated fatty acid composition of skeletal muscle membranes and insulin sensitivity. More detailed
analysis has indicated that the activity of Δ5 desaturase is inversely correlated to insulin resistance. The amount of docosahexaenoic
acid (C22:6n3) is also thought to play a part in determining insulin sensitivity. The purpose of this study was to test the
hypothesis that early growth retardation in the rat, as a result of maternal protein restriction, would lead to alterations
in desaturase activities similar to those observed in human insulin resistance. There were no differences in phospholipid
fatty acid composition in liver or muscle from control and low protein rats. In both muscle and liver the ratio of docosahexaenoic
acid to docosapentaenoic acid was, however, reduced in low protein offspring. Direct measurement of Δ5 desaturase activity
in hepatic microsomes showed a reduction ( p < 0.03) in the low protein offspring which was negatively corrrelated ( r = – 0.855) with fasting plasma insulin. No correlation was observed in controls. These results show that it is possible to
programme the activity of key enzymes involved in the desaturation of long chain polyunsaturated fatty acids. This is possibly
a mechanism linking fetal growth retardation to insulin resistance. [Diabetologia (1998) 41: 1337–1342]
Received: 25 March 1998 and in final revised form: 17 June 1998 相似文献
13.
Aims/hypothesis Insulin resistance in skeletal muscle is a hallmark of type 2 diabetes. Therefore, we sought to identify and validate genes
involved in the development of insulin resistance in skeletal muscle.
Materials Differentially regulated genes in skeletal muscle of male obese insulin-resistant, and lean insulin-sensitive Zucker diabetic
fatty (ZDF) rats were determined using Affymetrix microarrays. Based on these data, various aspects of glucose disposal, insulin
signalling and fatty acid composition were analysed in a muscle cell line overexpressing stearoyl-CoA desaturase 1 (SCD1).
Results Gene expression profiling in insulin-resistant skeletal muscle revealed the most pronounced changes in gene expression for
genes involved in lipid metabolism. Among these, Scd1 showed increased expression in insulin-resistant animals, correlating with increased amounts of palmitoleoyl-CoA. This was
further investigated in a muscle cell line that overexpressed SCD1 and accumulated lipids, revealing impairments of glucose
uptake and of different steps of the insulin signalling cascade. We also observed differential effects of high-glucose and
fatty acid treatment on glucose uptake and long-chain fatty acyl-CoA profiles, and in particular an accumulation of palmitoleoyl-CoA
in cells overexpressing SCD1.
Conclusions/interpretation Insulin-resistant skeletal muscle of ZDF rats is characterised by a specific gene expression profile with increased levels
of Scd1. An insulin-resistant phenotype similar to that obtained by treatment with palmitate and high glucose can be induced in vitro
by overexpression of SCD1 in muscle cells. This supports the hypothesis that elevated SCD1 expression is a possible cause
of insulin resistance and type 2 diabetes.
Electronic supplementary material Supplementary material is available for this article at and accessible for authorised users. 相似文献
14.
Aims/hypothesis: This study investigated the expression of adipose tissue fatty acid binding proteins (FABPs) in subcutaneous and visceral
human adipose tissue depots from lean and obese individuals.
Methods: Adipocyte lipid binding protein (ALBP) and keratinocyte lipid binding protein (KLBP) expression was quantified by western
blot in subcutaneous and omental adipose tissue from 20 obese and 9 lean individuals. RNA expression was quantified by Northern
blot in the obese subjects.
Results: In the obese subjects, ALBP protein and RNA expression was higher in subcutaneous compared with omental adipose tissue (increases
of 31 ± 14 % and 40 ± 13 % respectively, both p < 0.05), whereas in the lean group, KLBP protein levels were 32 ± 9 % lower in subcutaneous fat ( p < 0.03). However, the ALBP/KLBP ratio was greater in subcutaneous compared to omental adipose tissue from both lean and obese
subjects: increases of 187 ± 71 % ( p = 0.01) and 52 ± 23 % ( p = 0.17) respectively for the protein ratio, and 21 ± 6 % for RNA ( p = 0.01, obese individuals). In lean subjects, insulin concentrations correlated positively with the ALBP/KLBP protein ratio
in both depots (both p≤ 0.03).
Conclusion/interpretation: There are regional differences in adipose tissue FABP expression, which could be influenced by obesity. However, the ALBP/KLBP
ratio is greater in subcutaneous than visceral adipose tissue in lean as well as in obese subjects. Investigation of adipose
tissue FABPs could further our understanding of the role of fatty acids in the insulin resistance syndrome. [Diabetologia
(2001) 44: 1268–1273]
Received: 1 February 2001 and in revised form: 25 June 2001 相似文献
15.
Dietary supplementation with conjugated linoleic acid (CLA) has been shown to reduce body fat mass. To investigate the effects of individual CLA isomers on the fatty acid profiles of lipogenic (liver and white adipose) and lipid sensitive (erythrocyte) tissues, BALB/c mice were fed with 1 of 2 diets supplemented with either a c9,t11-CLA-enriched and t10,c12-CLA-free or a CLA-mixture containing both isomers in equal amounts (1% w/w of the diet) for 5 weeks. A control group was fed with a diet enriched in sunflower oil to energy balance the CLA. Compared to the t10,c12-CLA-free and the control diets, we observed a significant reduction of adipose tissue accompanied by fatty livers in the CLA-mix-fed group. These alterations in body fat distribution entailed a conspicuous shift of the fatty acid profiles of adipose tissue and livers. Liver enlargement was mainly caused by accumulation of C18 monoenes that accounted for 67 ± 1% of total fatty acid methyl esters. The significant reduction of the 18:0/18:1 desaturation index in the liver upon CLA-mix diet indicated high stearoyl-CoA desaturase activity. In contrast, reduction in white adipose tissue was largely driven by percental reduction of monounsaturated fatty acids (p ≤ 0.001). 16:0/ 16:1 and 18:0/18:1 desaturation indices for white adipose tissue significantly increased, suggesting an inhibition of stearoyl-CoA desaturase upon CLA-mix diet. The fatty acid profile of the erythrocytes widely reflected that of livers, depending on the supplemented diet. These profound changes in fatty acid composition of lipogenic organs due to t10,c12-CLA intake may be the consequence of functional alterations of lipid metabolism. 相似文献
16.
We demonstrate that naturally occurring C(14) and C(16)-specific acyl-acyl carrier protein (ACP) desaturases from plants can complement the unsaturated fatty acid (UFA) auxotrophy of an Escherichia coli fabA/fadR mutant. Under the same growth conditions, C(18)-specific delta(9)-stearoyl (18:0)-ACP desaturases are unable to complement the UFA auxotrophy. This difference most likely results from the presence of sufficient substrate pools of C(14) and C(16) acyl-ACPs but a relative lack of C(18) acyl-ACP pools in E. coli to support the activities of the plant fatty acid desaturase. Based on this, a substrate-dependent selection system was devised with the use of the E. coli UFA auxotroph to isolate mutants of the castor delta(9)-18:0-ACP desaturase that display enhanced specificity for C(14) and C(16) acyl-ACPs. Using this selection system, a number of desaturase variants with altered substrate specificities were isolated from pools of randomized mutants. These included several G188L mutant isolates, which displayed a 15-fold increase in specific activity with 16:0-ACP relative to the wild-type castor delta(9)-18:0-ACP desaturase. Expression of this mutant in Arabidopsis thaliana resulted in the accumulation of unusual monounsaturated fatty acids to amounts of >25% of the seed oil. The bacterial selection system described here thus provides a rapid means of isolating variant fatty acid desaturase activities for modification of seed oil composition. 相似文献
17.
Acyl-acyl carrier protein (ACP) desaturases introduce double bonds at specific positions in fatty acids of defined chain lengths and are one of the major determinants of the monounsaturated fatty acid composition of vegetable oils. Mutagenesis studies were conducted to determine the structural basis for the substrate and double bond positional specificities displayed by acyl-ACP desaturases. By replacement of specific amino acid residues in a Δ 6-palmitoyl (16:0)-ACP desaturase with their equivalents from a Δ 9-stearoyl (18:0)-ACP desaturase, mutant enzymes were identified that have altered fatty acid chain-length specificities or that can insert double bonds into either the Δ 6 or Δ 9 positions of 16:0- and 18:0-ACP. Most notably, by replacement of five amino acids (A181T/A200F/S205N/L206T/G207A), the Δ 6-16:0-ACP desaturase was converted into an enzyme that functions principally as a Δ 9-18:0-ACP desaturase. Many of the determinants of fatty acid chain-length specificity in these mutants are found in residues that line the substrate binding channel as revealed by x-ray crystallography of the Δ 9-18:0-ACP desaturase. The crystallographic model of the active site is also consistent with the diverged activities associated with naturally occurring variant acyl-ACP desaturases. In addition, on the basis of the active-site model, a Δ 9-18:0-ACP desaturase was converted into an enzyme with substrate preference for 16:0-ACP by replacement of two residues (L118F/P179I). These results demonstrate the ability to rationally modify acyl-ACP desaturase activities through site-directed mutagenesis and represent a first step toward the design of acyl-ACP desaturases for the production of novel monounsaturated fatty acids in transgenic oilseed crops. 相似文献
18.
Tissue availability of polyunsaturated fatty acids (PUFAs) depends on dietary intake and metabolic turnover and has a major impact on human health. Strong associations between variants in the human genes fatty acid desaturase 1 ( FADS1, encoding Δ-5 desaturase) and fatty acid desaturase 2 ( FADS2, encoding Δ-6 desaturase) and blood levels of PUFAs and long-chain PUFAs (LC-PUFAs) have been reported. The most significant associations and the highest proportion of genetically explained variability (28%) were found for arachidonic acid (20:4n-6), the main precursor of eicosanoids. Subjects carrying the minor alleles of several single nucleotide polymorphisms had a lower prevalence of allergic rhinitis and atopic eczema. Therefore, blood levels of PUFAs and LC-PUFAs are influenced not only by diet, but to a large extent also by genetic variants common in a European population. These findings have been replicated in independent populations. Depending on genetic variants, requirements of dietary PUFA or LC-PUFA intakes to achieve comparable biological effects may differ. We recommend including analyses of FADS1 and FADS2 polymorphism in future cohort and intervention studies addressing biological effects of PUFAs and LC-PUFAs. 相似文献
19.
Aims/hypothesis Adiponectin is important in the regulation of insulin sensitivity in man. Its receptors, adipoR1 and R2, have recently been identified, but their expression in adipose tissue and their regulation in response to insulin sensitisation of diabetic patients have never been assessed. We therefore explored the regulation of adipoR1/R2 and adiponectin expression in adipose tissue and skeletal muscle, and of adiponectin plasma concentrations in response to insulin sensitisation by rosiglitazone.Methods Patients with type 2 diabetes were studied in a double-blind, placebo-controlled crossover study, using in vivo arteriovenous techniques of measuring adipose tissue and muscle blood flow, combined with measurement of adipose tissue and skeletal muscle gene expression.Results Rosiglitazone treatment increased adiponectin concentrations by 69%. Skeletal muscle adipoR1 expression was down-regulated from 109.0 (70.1–165.7) (median [interquartile range]) to 82.8 (63.6–89.3) relative units ( p=0.04), but adipose tissue adipoR1 expression was up-regulated from 5.3 (4.4–9.4) to 11.2 (4.8–15.3) relative units ( p=0.02) by rosiglitazone. In contrast to adipoR1 expression, adipoR2 expression was not altered by rosiglitazone in either of the tissues. The increase in adipose tissue adipoR1 expression with rosiglitazone was associated with increased postprandial triglyceride clearance ( r=0.67, p=0.05), and increased fasting fatty acid output ( r=0.78, p=0.01) measured in subcutaneous adipose tissue.Conclusions/interpretation AdipoR1 expression is up-regulated in adipose tissue but down-regulated in skeletal muscle by rosiglitazone. These data suggest that adipoR1 plays a role in mediating the effects of adiponectin in specific tissues in relation to insulin sensitisation.G. D. Tan, and C. Debard contributed equally to this work. 相似文献
20.
The ratio of unsaturated to saturated long-chain fatty acids (LC-FAs) in skeletal muscle has been associated with insulin resistance. Some animal data suggest a modulatory effect of peroxisome proliferator receptor γ (PPARγ) stimulation on stearoyl-CoA desaturase 1 (SCD1) and LC-FA composition in skeletal muscle, but human data are rare. We here investigate whether treatment with a PPARγ agonist affects myocellular SCD1 expression and modulates the intramyocellular fatty acid profile in individuals with impaired glucose tolerance. Muscle biopsies and hyperinsulinemic-euglycemic clamps were performed in 7 men before and after 8 weeks of rosiglitazone treatment. Intramyocellular saturated, monounsaturated, and polyunsaturated intramuscular fatty acid profiles were measured by gas chromatography. Effects on SCD1 messenger RNA expression were analyzed in C2C12 cells and in human biopsies before and after rosiglitazone treatment. As expected, treatment with the PPARγ activator rosiglitazone improved insulin sensitivity in humans. Myocellular SCD1 messenger RNA expression was increased in human biopsies and C2C12 cells. Although the total content of myocellular LC-FA was unchanged, a relative shift from saturated LC-FAs to unsaturated LC-FAs was observed in human biopsies. Particularly, the amount of stearate was reduced, whereas the amounts of palmitoleate as well as oleate and vaccenate were increased, after rosiglitazone therapy. These changes resulted in an increased fatty acid Δ9-desaturation index (16:1/16:0 and 18:1/18:0) in skeletal muscle and a decreased elongase activity index (18:0/16:0). The PPARγ associated phenotypes may be partially explained by an increased Δ9-desaturation and a decreased elongase activity of skeletal muscle. 相似文献
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