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ORIGINAL RESEARCH COMMUNICATION |
1 From the Nutrition Food and Health Research Centre, Kings College London (TABS and TdG); the Medical Research Council Cardiovascular Research Group, Wolfson Institute, Royal London & St Bartholomews Hospital Medical School, London (GJM); and the Centre for the Genetics of Cardiovascular Disease, British Heart Foundation Laboratories, Royal Free and University College London Medical School, London (JA and SEH).
2 Supported by the Ministry of Agriculture, Fisheries and Food Dietary: Lipids Research Programme (project AN0219); the British Heart Foundation (grant RG2000/015); and the Medical Research Council. 3 Reprints not available. Address correspondence to TAB Sanders, Nutrition Food and Health Research Centre, Kings College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NN, United Kingdom. E-mail: tom.sanders{at}kcl.ac.uk.
| ABSTRACT |
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Objective: The goal was to determine whether plasminogen activator inhibitor 1 (PAI-1) and fibrinolytic activities are influenced by 1) dietary fat intake from a test meal and 2) the PAI-1 4G allele.
Design: A parallel randomized controlled trial was used to compare the effect on fibrinolytic activity, measured as dilute clot lysis time, of high-oleate or high-palmitate test meals (both containing 50 g fat; both n = 18) with that of a low-fat test meal (15 g fat; n = 15) in men aged > 52 y. In a second study, postprandial changes in PAI-1 activity were measured in 32 men in response to a high-oleate meal containing 50 g fat. The results from both studies were analyzed according to PAI-1 4G-675/5G genotype.
Results: Fasting dilute clot lysis time was positively associated with body mass index (r = 0.326, P = 0.02) and was shortened postprandially (P < 0.00001) independent of the fat content of the meal. Fasting PAI-1 activity was higher in those carrying the 4G allele and was correlated with fasting plasma triacylglycerol concentrations (r = 0.48, P = 0.008) and factor VII coagulant activity (r = 0.46, P = 0.012) after adjustments for age, body mass index, and genotype. Plasma PAI-1 activity decreased significantly after a meal but was not associated with postprandial changes in plasma triacylglycerols after a high-fat meal. The postprandial increase in plasma triacylglycerols was higher in subjects carrying the 4G allele.
Conclusion: Fibrinolytic activity is not lower after meals rich in palmitate or oleate than after a low-fat meal.
Key Words: Plasminogen activator inhibitor 1 PAI-1 monounsaturated fatty acids saturated fatty acids PAI 4G-675/5G fibrinolysis
| INTRODUCTION |
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The presence of a 4G allele at a common insertion-deletion polymorphism in the promoter of the PAI-1 gene has been associated with elevated plasma PAI-1 concentration and activity (5) and also with inducible expression of PAI-1 in response to interleukin 1 (6). Carriers of the 4G allele may be at increased risk of ischemic heart disease (7, 8), but this may be dependent on an interaction with other environmental factors, which may explain why results in Western populations have been equivocal (5, 9). In one study, an increase in PAI-1 activity was reported 8 h after a test meal very high in butter fat in subjects carrying the 4G allele but not in those with the 5G/5G genotype (10). The aims of the present study were to compare, in middle-aged men, the acute effects of meals high in palmitate or oleate with those of a low-fat meal on fibrinolytic activity measured by the DCLT method and to determine PAI-1 activity during fasting and in response to a high-oleate meal according to PAI-1 genotype.
| SUBJECTS AND METHODS |
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In the first study, 54 men selected on the basis of having nonfasting triacylglycerol concentrations > 2 mmol/L were recruited to compare the effects of test meals high in oleate or palmitate with those of a low-fat diet on fibrinolytic activity measured by using the DCLT method. In the second study, the subjects were selected on the basis of their factor VII R353Q genotype (11); measurements of PAI-1 activity were made in response to a test meal high in oleate, and comparisons were made post hoc with PAI-1 genotype. Subjects were invited by letter to take part in the test meal studies and received no remuneration for their cooperation in the study. Background medication use, blood pressure, nonfasting plasma triacylglycerol and cholesterol concentrations, and body mass index (BMI; in kg/m2) were extracted from records of the subjects annual examination for the NPHS-II. The subjects generally had one or more risk factors (blood pressure > 140/90 mm Hg, serum cholesterol > 5.2 mmol/L, or current smoker).
The subjects were requested to avoid foods high in fat on the day preceding the test meal study and to avoid strenuous exercise. They were given a list of foods to avoid and were asked to fast from 2200 overnight. The following morning, a fasting venous blood sample for determination of DCLT and plasma triacylglycerol concentrations was taken in the clinic of the general practice. The subjects were then provided with a test meal that they consumed within 20 min. Further venous blood samples were obtained 3 and 6 h postprandially for the same measurements. After the 3-h postprandial venous sample had been taken, the subjects were provided with a low-fat lunch (yogurt and a piece of fruit). The subjects were advised to avoid any strenuous activity throughout the study period but were allowed to leave the clinic to return home or to work between blood samplings.
To compare the effects of palmitate- and oleate-rich meals with those of a low-fat meal, we randomly allocated the subjects into 3 groups of 18 each. The high-fat test meals contained 50 g fat provided either as higholeic acid sunflower oil or as palm oil and the low-fat meal contained 15 g fat (higholeic acid sunflower oil). The test meals were previously described (11). The high-oleate test meal provided 40 g 18:1n-9, 5 g 18:2n-6, 2 g 18:0, and 2 g 16:0; the high-palmitate test meal provided 20 g 18:1n-9, 5 g 18:2n-6, 2 g 18:0, and 22 g 16:0; and the low-fat test meal provided 11.9 g 18:1n-9; 1.4 g 18:2n-6, 0.6 g 18:0, and 0.6 g 16:0.
Venous blood samples were collected by using the evacuated tube technique with minimal compression necessary to display the vein. The first 4.5 mL blood was drawn into a tube containing EDTA. Plasma was separated by centrifugation at 1500 x g for 15 min at 4 °C and was stored at 4 °C for determination of triacylglycerols within 48 h by enzymatic assay (GPO-PAP; Roche Diagnostics, Lewes, East Sussex, United Kingdom). For determination of fibrinolytic activity, blood was collected into 0.5 mL solution containing 38 g trisodium citrate/L at room temperature and centrifuged at 1000 x g for 15 min at 20 °C and plasma was separated. The sample was transferred to the main laboratory for measurement of DCLT on the same day (12).
In the second study, an aliquot of plasma was frozen and stored initially at -40 °C and then at -70 °C until analyzed for PAI-1 activity by chromogenic assay (Chromogenix AB, Mölndal, Sweden). DNA was isolated from white blood cells and amplified by polymerase chain reaction, and PAI-1 genotype was determined as previously described (13). Factor VII coagulant activity (FVII:c) was reported previously (11).
Statistical analyses of the data were conducted by using SPSS/PC, version 10 (SPSS Inc, Chicago), and PRISM, version 3.02 (GraphPad Software Inc, San Diego) for nonparametric statistics. The DCLT data were analyzed as follows: comparisons between treatments were made by using the Kruskal Wallis test, changes with time were analyzed by using Friedmans test, and changes from fasting values within each treatment were analyzed by using Dunns test. Data for plasma triacylglycerols and PAI-1 were analyzed by repeated-measures analysis of variance with age and BMI entered as covariates. When there was a significant genotype effect, separate analyses were conducted for each genotype. Comparisons between time points were made by using Bonferonnis multiple comparison test.
| RESULTS |
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| DISCUSSION |
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In contrast with the findings of the present study, Byrne et al (10) reported an increase in PAI-1 activity after a high-fat meal. In that study, the subjects had an in-dwelling catheter and thus were relatively immobile. Because physical activity acutely decreases PAI-1 activity (19), immobility might have accounted for the increase in PAI-1 activity reported in that study. However, the amount of fat used in the test meal was much higher (130 g) than in the present study, and the type of fat also differed (butter fat). In that study, PAI-1 activity differed after the test meal between subjects carrying the 4G allele and subjects homozygous for the 5G allele by an increase of
4 units/mL. This difference is similar to that in PAI-1 activity between genotypes in the present study.
Our results are consistent with recent reports that there is significant diurnal variation in carriers of the 4G allele compared with subjects homozygous for the 5G allele (20, 21). The reasons for the diurnal variations in PAI-1 activity are uncertain.
A novel observation that requires confirmation was the finding of a lower plasma triacylglycerol concentration in the subjects homozygous for the 5G allele. We did not analyze the data for the comparison in the first study because the subjects were selected on the basis of their nonfasting serum triacylglycerol concentrations.
In common with previous reports, we observed that PAI-1 activity was positively associated with fasting plasma triacylglycerol concentrations (3). However, because the elevation in plasma triacylglycerols after a high-fat meal was accompanied by a decrease in PAI-1 activity, this implies that the association between fasting plasma triacylglycerols and PAI-1 activity is not causal and may be related to the underlying cause of elevated fasting plasma triacylglycerols, most likely insulin resistance. Although we did not measure plasma insulin or glucose in these subjects, we found that FVIIc, another index of the insulin resistance syndrome, was also positively correlated with PAI-1 activity. These findings are consistent with the observation that weight loss associated with decreased energy intake (4) and regular physical activity (22) results in improvement in fibrinolytic activity.
These data confirm the findings of many previous reports that PAI-1 activity in 5G/5G subjects is 4050% lower than that in subjects who carry one or more 4G alleles (5, 6, 20, 21). However, the diurnal variations appeared to be greater in subjects with one or more 4G allele. This could be an important source of confounding in studies assessing diet-genotype interactions with regard to PAI-1. Meta-analysis of published studies show that the PAI-1 promoter 4G variant is associated with a 30% higher risk of myocardial infarction than that in 5G/5G subjects (23), with little evidence of heterogeneity of effect in subjects from different countries who might be expected to have different dietary habits. In summary, the data in the present study show that postprandial variations in fibrinolytic activity are modulated by the PAI-1 4G-675/5G genotype but not by the fat content of a meal.
| ACKNOWLEDGMENTS |
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TABS and GJM were the principal investigators and contributed to the design, interpretation, and writing of the manuscripts, TdG recruited the subjects, designed the test meals, and undertook the dilute clot lysis activity measurements. JA undertook the PAI-1 genotyping analyses, and SEH contributed to the writing of the manuscript. None of the authors had any conflicts of interests.
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