64 resultados para Low Density Lipoprotein Receptor-Related Protein-6


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The aim of the current study was to investigate the antioxidant and cellular activity of the olive oil phenolics oleuropein, tyrosol, hydroxytyrosol, and homovanillic alcohol (which is also a major metabolite of hydroxytyrosol). Well-characterized chemical and biochemical assays were used to assess the antioxidant potential of the compounds. Further experiments investigated their influence in cell culture on cytotoxic effects of hydrogen peroxide and oxidized low-density lipoprotein (LDL), nitric oxide production by activated macrophages, and secretion of chemoattractant and cell adhesion molecules by the endothelium. Inhibitory influences on in vitro platelet aggregation were also measured. The antioxidant assays indicated that homovanillic alcohol was a significantly more potent antioxidant than the other phenolics, both in chemical assays and in prolonging the lag phase of LDL oxidation. Cell culture experiments suggested that the olive oil phenolics induce a significant reduction in the secretion of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 (and a trend towards a reduced secretion of monocyte chemoattractant protein-1), and protect against cytotoxic effects of hydrogen peroxide and oxidized LDL. However, no influence on nitric oxide production or platelet aggregation was evident. The data show that olive oil phenolics have biochemical and cellular actions, which, if also apparent in vivo, could exert cardioprotective effects.

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Objective: To determine whether consumption of five portions of fruit and vegetables per day reduces the enhancement of oxidative stress induced by consumption of fish oil. Subjects: A total of 18 free-living healthy smoking volunteers, aged 18-63 y, were recruited by posters and e-mail in The University of Reading, and by leaflets in local shops. Design: A prospective study. Setting: Hugh Sinclair Unit of Human Nutrition, School of Food Biosciences, The University of Reading, Whiteknights PO Box 226, Reading RG6 6AP, UK. Intervention: All subjects consumed a daily supplement of 4 x 1 g fish oil capsules for 9 weeks. After 3 weeks, they consumed an additional five portions of fruits and vegetables per day, and then they returned to their normal diet for the last 3 weeks of the study. Fasting blood samples were taken at the ends of weeks 0, 3, 6 and 9. Results: The plasma concentrations of ascorbic acid, lutein, beta-cryptoxanthin, alpha-carotene and beta-carotene all significantly increased when fruit and vegetable intake was enhanced (P<0.05). Plasma concentrations of α-tocopherol, retinol and uric acid did not change significantly during the period of increased fruit and vegetable consumption. Plasma oxidative stability, assessed by the oxygen radical absorbance capacity (ORAC) assay, also increased from weeks 3-6 (P<0.001) but not in association with increases in measured antioxidants. Lag phase before oxidation of low-density lipoprotein (LDL) significantly decreased in the first 3 weeks of the study, reflecting the incorporation of EPA and DHA into LDL (P<0.0001). Subsequent enhanced fruit and vegetable consumption significantly reduced the susceptibility of LDL to oxidation (P<0.005). Conclusion: Fish oil reduced the oxidative stability of plasma and LDL, but the effects were partially offset by the increased consumption of fruit and vegetables.

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Protein-bound glutathione (PSSG) and protein-bound related thiol compounds, i.e. cysteine (PSSCys), glutamyl-cysteine (PSSGlu-Cys) and cysteinyl-glycine (PSSCys-Gly), were analysed in proteins of Osborne fractions, i.e. gliadin, glutenin and gliadin-, glutenin-subfractions separated by gel filtration chromatography, gel protein and the total gluten proteins separated from wheat varieties with varying breadmaking performances. The results showed that PSSG and some protein-bound related thiol compounds were found in monomeric gliadins, indicating that glutathione and some related thiol compounds are able to form disulphide bonds (SS) with sulphydryl group (SH) of those proteins and the formation of those disulphide bonds may prevent those monomeric proteins from binding to other proteins. It was also observed that a larger amount of PSSG in glutenin proteins was negatively correlated with the molecular weight (M-w) distribution of glutenin polymers, suggesting that PSSG and protein-bound related thiol compounds may play an important role in controlling polymerisation of glutenin. Furthermore, it was found that the level of PSSG in gel protein from flours with poor breadmaking performances was constantly higher and significantly different (p < 0.05) from that of flours with good breadmaking performance. The same trend was observed with gluten samples from breadmaking and biscuitmaking flours. (C) 2003 Elsevier Ltd. All rights reserved.

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Objective: To determine whether dietary supplementation with a natural carotenoid mixture counteracts the enhancement of oxidative stress induced by consumption of fish oil. Design: A randomised double-blind crossover dietary intervention. Setting: Hugh Sinclair Unit of Human Nutrition, School of Food Biosciences, The University of Reading, Whiteknights PO Box 226, Reading RG6 6AP, UK. Subjects and intervention: A total of 32 free-living healthy nonsmoking volunteers were recruited by posters and e-mails in The University of Reading. One volunteer withdrew during the study. The volunteers consumed a daily supplement comprising capsules containing fish oil (4 x 1 g) or fish oil (4 x 1 g) containing a natural carotenoid mixture (4 x 7.6 mg) for 3 weeks in a randomised crossover design separated by a 12 week washout phase. The carotenoid mixture provided a daily intake of beta-carotene (6.0 mg), alpha-carotene (1.4 mg), lycopene (4.5 mg), bixin (11.7 mg), lutein (4.4 mg) and paprika carotenoids (2.2 mg). Blood and urine samples were collected on days 0 and 21 of each dietary period. Results: The carotenoid mixture reduced the fall in ex vivo oxidative stability of low-density lipoprotein (LDL) induced by the fish oil (P = 0.045) and it reduced the extent of DNA damage assessed by the concentration of 8-hydroxy-2'-deoxyguanosine in urine (P = 0.005). There was no effect on the oxidative stability of plasma ex vivo assessed by the oxygen radical absorbance capacity test. beta- Carotene, alpha-carotene, lycopene and lutein were increased in the plasma of subjects consuming the carotenoid mixture. Plasma triglyceride levels were reduced significantly more than the reduction for the fish oil control (P = 0.035), but total cholesterol, HDL and LDL levels were not significantly changed by the consumption of the carotenoid mixture. Conclusions: Consumption of the natural carotenoid mixture lowered the increase in oxidative stress induced by the fish oil as assessed by ex vivo oxidative stability of LDL and DNA degradation product in urine. The carotenoid mixture also enhanced the plasma triglyceride-lowering effect of the fish oil.

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Aim: We examined the effect of meat fatty acids on lipid and apolipoprotein concentrations of very low density lipoprotein (VLDL) and chylomicron/chylomicron remnants in lipid fractions with a Svedberg flotation rate (S-f) 60-400 and S-f 20-60. Methods and results: Six healthy middle-aged men received in random order mixed meals enriched with saturated (SFA), polyunsaturated (PUFA) or monounsaturated (MUFA) fatty acids on 3 occasions. VLDL and chylomicron/chylomicron remnants in the lipid fractions were separated by immunoaffinity chromatography against apo B-100. In the S-f 60-400 chylomicron/chylomicron remnants, triacylglycerol and cholesterol concentrations were significantly tower following PUFA compared with SFA and MUFA (P <= 0.05). Apolipoprotein (apo) E responses were significantly higher after SFA in chylomicron/chylomicron remnants and VLDL compared with PUFA and MUFA (P < 0.007). However, apo B responses (particle number) were higher following MUFA than SFA (P = 0.039 for chylomicron/chylomicron remnants). Composition of the chylomicron/chylomicron remnants (expressed per particle) revealed differences in their triacylglycerol and apo E contents; in the Sf 60-400 fraction, SFA-rich chylomicron/chylomicron remnants contained significantly more triacylglycerol than MUFA (P = 0.028), more apo E than PUFA- and MUFA-rich particles (P < 0.05) and in the S-f 20-60 fraction, more apo E than MUFA (P = 0.009). Conclusion: There are specific differences in the composition of chylomicron/ chylomicron remnants formed after saturated compared with unsaturated fatty acid-rich meals which could determine their metabolic fate in the circulation and subsequent atherogenicity. (C) 2005 Elsevier B.V. All rights reserved.

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The ability of human postprandial triacylglycerol-rich lipoproteins (TRLs), isolated after meals enriched in saturated fatty acids (SFAs), n-6 PUFAs, and MUFAs, to inhibit the uptake of I-125-labeled LDL by the LDL receptor was investigated in HepG2 cells. Addition of TRLs resulted in a dose-dependent inhibition of heparin-releasable binding, cell-associated radioactivity, and degradation products of I-125-labeled LDL (P < 0.001). SFA-rich Svedberg flotation rate (S-f) 60-400 resulted in significantly greater inhibition of cell-associated radioactivity than PUFA-rich particles (P = 0.016) and total uptake of I-125-labeled LDL compared with PUFA- and MUFA-rich particles (P = 0.02). Normalization of the apolipoprotein (apo)E but not apoC-III content of the TRLs removed the effect of meal fatty acid composition, and addition of an anti-apoE antibody reversed the inhibitory effect of TRLs on the total uptake of I-125-labeled LDL. Real time RT-PCR showed that the SFA-rich Sf 60-400 increased the expression of genes involved in hepatic lipid synthesis (P < 0.05) and decreased the expression of the LDL receptor-related protein 1 compared with MUFAs (P = 0.008). In conclusion, these findings suggest an alternative or additional mechanism whereby acute fat ingestion can influence LDL clearance via competitive apoE-dependent effects of TRL on the LDL receptor.-Jackson, K. G., V. Maitin, D. S. Leake, P. Yaqoob, and C. M. Williams. Saturated fat-induced changes in Sf 60 400 particle composition reduces uptake of LDL by HepG2 cells.

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Background and purpose: The aim of this report is to study mechanisms of G protein activation by agonists. Experimental approach: The association and dissociation of guanosine 5'-O-(3-[S-35] thio) triphosphate ([S-35] GTP gamma S) binding at G proteins in membranes of CHO cells stably transfected with the human dopamine D-2short receptor was studied in the presence of a range of agonists. Key results: Binding of [S-35] GTPgS was dissociable in the absence of agonist and dissociation was accelerated both in rate and extent by dopamine, an effect which was blocked by the dopamine D-2 receptor antagonist raclopride and by suramin, which inhibits receptor/G protein interaction. A range of agonists of varying efficacy increased the rate of dissociation of [S-35] GTPgS binding, with the more efficacious agonists resulting in faster dissociation. Agonists were able to dissociate about 70% of the pre-bound [S-35] GTPgS, leaving a component which may not be accessible to the agonist-bound receptor. The dissociable component of the [S-35] GTPgS binding was reduced with longer association times and increased [S-35] GTPgS concentrations. Conclusions and implications: These data are consistent with [S-35] GTPgS binding being initially to receptor-linked G proteins and then to G proteins which have separated from the agonist bound receptor. Under the conditions used typically for [S-35] GTPgS binding assays, therefore, much of the agonist-receptor complex remains in proximity to G proteins after they have been activated by agonist.

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OBJECTIVE: To determine the effect of altering meal frequency on postprandial lipaemia and associated parameters. DESIGN: A randomized open cross over study to examine the programming effects of altering meal frequency. A standard test meal was given on three occasions following: (i) the normal diet; (ii) a period of two weeks on a nibbling and (iii) a period of two weeks on a gorging diet. SETTING: Free living subjects associated with the University of Surrey. SUBJECTS: Eleven female volunteers (age 22 +/- 0.89 y) were recruited. INTERVENTIONS: The subjects were requested to consume the same foods on either a nibbling diet (12 meals per day) or a gorging diet (three meals per day) for a period of two weeks. The standard test meal containing 80 g fat, 63 g carbohydrate and 20 g protein was administered on the day prior to the dietary intervention and on the day following each period of intervention. MAJOR OUTCOME MEASURES: Fasting and postprandial blood samples were taken for the analysis of plasma triacylglycerol, non-esterified fatty acids, glucose, immunoreactive insulin, glucose-dependent insulinotropic polypeptide levels (GIP) and glucagon-like peptide (GLP-1), fasting total, low density lipoprotein (LDL)- and high density lipoprotein (HDL)-cholesterol concentrations and postheparin lipoprotein lipase (LPL) activity measurements. Plasma paracetamol was measured following administration of a 1.5 g paracetamol load with the meal as an index of gastric emptying. RESULTS: The compliance to the two dietary regimes was high and there were no significant differences between the nutrient intakes on the two intervention diets. There were no significant differences in fasting or postprandial plasma concentrations of triacylglycerol, non-esterified fatty acids, glucose, immunoreactive insulin, GIP and GLP-1 levels, in response to the standard test meal following the nibbling or gorging dietary regimes. There were no significant differences in fasting total or LDL-cholesterol concentrations, or in the 15 min postheparin lipoprotein lipase activity measurements. There was a significant increase in HDL-cholesterol in the subjects following the gorging diet compared to the nibbling diet. DISCUSSION: The results suggest that previous meal frequency for a period of two weeks in young healthy women does not alter the fasting or postprandial lipid or hormonal response to a standard high fat meal. CONCLUSIONS: The findings of this study did not confirm the previous studies which suggested that nibbling is beneficial in reducing the concentrations of lipid and hormones. The rigorous control of diet content and composition in the present study compared with others, suggest reported effects of meal frequency may be due to unintentional alteration in nutrient and energy intake in previous studies.

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The present study reports results from two investigations to determine effects of a 6-week period of moderate n-3 fatty acid supplementation (2.7 g/d) on fasting and on postprandial triacylglycerol and metabolic hormone concentrations in response to standard test meals. In the first study postprandial responses were followed for 210 min after an early morning test meal challenge; in the second study responses to an evening test meal were followed during the evening and overnight for a total period of 12 h. In both studies postprandial triacylglycerol responses to the test meals were significantly reduced after compared with before fish-oil supplementation. In the second study the triacylglycerol peak response seen between 200 and 400 min in subjects studied before supplementation with fish oils was almost completely absent in the same subjects after 6 weeks of n-3 fatty acid supplementation. Analysis of fasting concentrations of metabolites and hormones was carried out on the combined data from the two studies. There were no significant differences in total, low-density-lipoprotein- or high-density-lipoprotein-cholesterol concentrations during fish-oil supplementation, although there was considerable individual variation in cholesterol responses to the supplement. Concentrations of Apo-B and Apo-A1 were unchanged during supplementation with fish oils. Fasting and early morning postprandial GIP concentrations were lower in subjects taking fish oils, possibly due to acute effects of fish-oil capsules taken on the evening before the studies. In both studies fasting insulin and glucose and postprandial insulin concentrations remained unchanged following fish-oil supplementation. The results do not support the view that triacylglycerol-lowering effects of n-3 fatty acids are due to modulation of insulin secretion mediated via the enteroinsular axis. Further studies are required to determine the precise mechanism by which fish oils reduce both fasting and postprandial triacylglycerol concentrations.

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Interest in effects of diet on postprandial lipoproteins has increased in recent years as a result of accumulating evidence for adverse cardiovascular consequences of elevated concentrations of triglyceride rich lipoproteins. Particular attention has been given to ability of different fatty acids to modulate postprandial lipoprotein responses because of evidence for both harmful and protective cardiovascular properties of the saturated, monounsaturated and ω-6 and ω-3 polyunsaturated fatty acid (PUFA) classes. Evidence for direct atherogenic properties of chylomicron remnants has led to attempts to monitor effects of diet specifically on this lipoprotein class. Limitations in the methods employed to measure chylomicron remnants and the small number of human studies which have evaluated effects of meal, and background diet, fatty acid composition, makes it difficult to draw definitive conclusions at the present time. However consideration of data from both animal and human studies tends to support the conclusion that diets, and meals, rich in PUFA (particularly long chain ω-3 PUFA), result in attenuated postprandial responses of the intestinally-derived lipoproteins. Attenuated responses to high PUFA meals appear to be due to greater rates of clearance and greater activation of lipoprotein lipase (LPL). Attenuated responses to high PUFA background diets may be due to adaptive changes involving both accelerated rates of clearance in peripheral tissues and liver, as well as decreased output of the competitor for chylomicron clearance, very low density lipoprotein (VLDL).

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OBJECTIVE: Circulating levels of 25-hydroxyvitamin D (25OHD) are positively associated with high density lipoprotein (HDL) cholesterol. We sought to replicate a previously reported interaction between APOA5 genotype and vitamin D, and to examine whether HDL-associated genetic loci modify the association between serum 25OHD and HDL cholesterol. METHODS: We examined whether 42 single nucleotide polymorphisms (SNPs) modify the association between serum 25OHD and HDL cholesterol in the 1958 British Birth cohort (aged 45 years, n = 4978). RESULTS: We identified a borderline interaction between the SNP rs12272004 (near the APOA5) and serum 25OHD on HDL cholesterol (P(interaction) = 0.05). The interaction was particularly prominent among the samples collected during winter (P(interaction) = 0.001). None of the other loci showed an interaction with serum 25OHD concentrations on HDL cholesterol. CONCLUSIONS: Our study in 4978 British Whites provides further support that APOA5 genotype modifies the association between vitamin D metabolites and HDL cholesterol.

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The first genome-wide association study for BMI identified a polymorphism, rs7566605, 10 kb upstream of the insulin-induced gene 2 (INSIG2) transcription start site, as the most significantly associated variant in children and adults. Subsequent studies, however, showed inconsistent association of this polymorphism with obesity traits. This polymorphism has been hypothesized to alter INSIG2 expression leading to inhibition of fatty acid and cholesterol synthesis. Hence, we investigated the association of the INSIG2 rs7566605 polymorphism with obesity- and lipid-related traits in Danish and Estonian children (930 boys and 1,073 girls) from the European Youth Heart Study (EYHS), a school-based, cross-sectional study of pre- and early pubertal children. The association between the polymorphism and obesity traits was tested using additive and recessive models adjusted for age, age-group, gender, maturity and country. Interactions were tested by including the interaction terms in the model. Despite having sufficient power (98%) to detect the previously reported effect size for association with BMI, we did not find significant effects of rs7566605 on BMI (additive, P = 0.68; recessive, P = 0.24). Accordingly, the polymorphism was not associated with overweight (P = 0.87) or obesity (P = 0.34). We also did not find association with waist circumference (WC), sum of four skinfolds, or with total cholesterol, triglycerides, low-density lipoprotein, or high-density lipoprotein. There were no gender-specific (P = 0.55), age-group-specific (P = 0.63) or country-specific (P = 0.56) effects. There was also no evidence of interaction between genotype and physical activity (P = 0.95). Despite an adequately powered study, our findings suggest that rs7566605 is not associated with obesity-related traits and lipids in the EYHS.

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Background: Public health strategies to lower cardiovascular disease (CVD) risk involve reducing dietary saturated fatty acid (SFA) intake to ≤10% of total energy (%TE). However, the optimal type of replacement fat is unclear. Objective: We investigated the substitution of 9.5-9.6%TE dietary SFA with either monounsaturated (MUFA) or n-6 polyunsaturated fatty acids (PUFA) on vascular function and other CVD risk factors. Design: Using a randomized, controlled, single-blind, parallel group dietary intervention, 195 men and women aged 21-60 y with moderate CVD risk (≥50% above the population mean) from the United Kingdom followed one of three 16-wk isoenergetic diets (%TE target compositions, total fat:SFA:MUFA:n-6 PUFA): SFA-rich (36:17:11:4, n = 65), MUFA-rich (36:9:19:4, n = 64) or n-6 PUFA-rich (36:9:13:10, n = 66). The primary outcome measure was flow-mediated dilatation (%FMD); secondary outcome measures included fasting serum lipids, microvascular reactivity, arterial stiffness, ambulatory blood pressure, and markers of insulin resistance, inflammation and endothelial activation. Results: Replacing SFA with MUFA or n-6 PUFA did not significantly impact on %FMD (primary endpoint) or other measures of vascular reactivity. Of the secondary outcome measures, substitution of SFA with MUFA attenuated the increase in night systolic blood pressure (-4.9 mm Hg, P = 0.019) and reduced E-selectin (-7.8%, P = 0.012). Replacement with MUFA or n-6 PUFA lowered fasting serum total cholesterol (TC; -8.4% and -9.2%, respectively), low-density lipoprotein cholesterol (-11.3% and -13.6%) and TC to high-density lipoprotein cholesterol ratio (-5.6% and -8.5%) (P ≤ 0.001). These changes in low-density lipoprotein cholesterol equate to an estimated 17-20% reduction in CVD mortality. Conclusions: Substitution of 9.5-9.6%TE dietary SFA with either MUFA or n-6 PUFA did not impact significantly on %FMD or other measures of vascular function. However, the beneficial effects on serum lipid biomarkers, blood pressure and E-selectin offer a potential public health strategy for CVD risk reduction.

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Rationale: Platelets are anuclear cell fragments derived from bone marrow megakaryocytes (MKs) that safeguard vascular integrity but may also cause pathological vessel occlusion. One major pathway of platelet activation is triggered by 2 receptors that signal through an (hem)immunoreceptor tyrosine-based activation motif (ITAM), the activating collagen receptor glycoprotein (GP) VI and the C-type lectin-like receptor 2 (CLEC-2). Growth factor receptor–bound protein 2 (Grb2) is a ubiquitously expressed adapter molecule involved in signaling processes of numerous receptors in different cell types, but its function in platelets and MKs is unknown. Objective: We tested the hypothesis that Grb2 is a crucial adapter protein in (hem)immunoreceptor tyrosine-based activation motif signaling in platelets. Methods and Results: Here, we show that genetic ablation of Grb2 in MKs and platelets did not interfere with MK differentiation or platelet production. However, Grb2-deficiency severely impaired glycoprotein VI–mediated platelet activation because of defective stabilization of the linker of activated T-cell (LAT) signalosome and activation of downstream signaling proteins that resulted in reduced adhesion, aggregation, and coagulant activity on collagen in vitro. Similarly, CLEC-2–mediated signaling was impaired in Grb2-deficient platelets, whereas the cells responded normally to stimulation of G protein–coupled receptors. In vivo, this selective (hem)immunoreceptor tyrosine-based activation motif signaling defect resulted in prolonged bleeding times but affected arterial thrombus formation only after concomitant treatment with acetylsalicylic acid, indicating that defective glycoprotein VI signaling in the absence of Grb2 can be compensated through thromboxane A2–induced G protein–coupled receptor signaling pathways. Conclusions: These results reveal an important contribution of Grb2 in (hem)immunoreceptor tyrosine-based activation motif signaling in platelets in hemostasis and thrombosis by stabilizing the LAT signalosome.

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Lipoprotein lipase (LPL) is a key rate-limiting enzyme for the hydrolysis of triacylglycerol (TAG) in chylomicrons and very low-density lipoprotein. Given that postprandial assessment of lipoprotein metabolism may provide a more physiological perspective of disturbances in lipoprotein homeostasis compared to assessment in the fasting state, we have investigated the influence of two commonly studied LPL polymorphisms (rs320, HindIII; rs328, S447X) on postprandial lipaemia, in 261 participants using a standard sequential meal challenge. S447 homozygotes had lower fasting HDL-C (p = 0.015) and a trend for higher fasting TAG (p = 0.057) concentrations relative to the 447X allele carriers. In the postprandial state, there was an association of the S447X polymorphism with postprandial TAG and glucose, where S447 homozygotes had 12% higher TAG area under the curve (AUC) (p = 0.037), 8.4% higher glucose-AUC (p = 0.006) and 22% higher glucose-incremental area under the curve (IAUC) (p = 0.042). A significant gene–gender interaction was observed for fasting TAG (p = 0.004), TAG-AUC (Pinteraction = 0.004) and TAG-IAUC (Pinteraction = 0.016), where associations were only evident in men. In conclusion, our study provides novel findings of an effect of LPL S447X polymorphism on the postprandial glucose and gender-specific impact of the polymorphism on fasting and postprandial TAG concentrations in response to sequential meal challenge in healthy participants