Sylvia A. de Jong

Impaired endothelial function following a meal rich in used cooking fat.

OBJECTIVES The purpose of this study was to test the hypothesis that intake of used cooking fat is associated with impaired endothelial function. BACKGROUND Diets containing high levels of lipid oxidation products may accelerate atherogenesis, but the effect on endothelial function is unknown. METHODS Flow-mediated endothelium-dependent dilation and glyceryl trinitrate-induced endothelium-independent dilation of the brachial artery were investigated in 10 men. Subjects had arterial studies before and 4 h after three test meals: 1) a meal (fat 64.4 g) rich in cooking fat that had been used for deep frying in a fast food restaurant; 2) the same meal (fat 64.4 g) rich in unused cooking fat, and 3) a corresponding low fat meal (fat 18.4 g) without added fat. RESULTS Endothelium-dependent dilation decreased between fasting and postprandial studies after the used fat meal (5.9 +/- 2.3% vs. 0.8 +/- 2.2%, p = 0.0003), but there was no significant change after the unused fat meal (5.3 +/- 2.1% vs. 6.0 +/- 2.5%) or low fat meal (5.3 +/- 2.3% vs. 5.4 +/- 3.3%). There was no significant difference in endothelium-independent dilation after any of the meals. Plasma free fatty acid concentration did not change significantly during any of the meals. The level of postprandial hypertriglyceridemia was not associated with change in endothelial function. CONCLUSIONS Ingestion of a meal rich in fat previously used for deep frying in a commercial fast food restaurant resulted in impaired arterial endothelial function. These findings suggest that intake of degradation products of heated fat contribute to endothelial dysfunction.

Reduced Postprandial Serum Paraoxonase Activity After a Meal Rich in Used Cooking Fat

Paraoxonase is an enzyme associated with HDL in human serum that hydrolyzes oxidized phospholipids and inhibits LDL oxidation, which is an important step in atherogenesis. In animals, addition of oxidized lipids to the circulation reduces paraoxonase activity, and diets rich in oxidized fat accelerate the development of atherosclerosis. The current randomized, crossover study was designed to compare the effect of a meal rich in oxidized lipids in the form of fat that had been used for deep-frying in a fast food restaurant and a control meal rich in the corresponding unused fat on postprandial serum paraoxonase (arylesterase) activity and peroxide content of LDL and its susceptibility to copper ion catalyzed oxidation in 12 healthy men. Four hours into the postprandial period, serum paraoxonase activity had decreased significantly after the used fat meal (-17%, P=0.005) and had increased significantly after the meal rich in unused fat (14%, P=0. 005). These changes were significantly (P=0.003) different. A time-course study indicated that serum paraoxonase activity remained lower than baseline for up to 8 hours after the used fat meal. Serum apoA1 concentration tended to decrease after the unused fat meal and tended to increase after the used fat meal. These changes were different at a marginal level of significance (P=0.07). Also, a significantly (P=0.03) greater decrease in apoA1 content of postprandial HDL was recorded after the unused fat meal. The peroxide content of LDL tended to decrease after the used fat meal and tended to increase after the control meal. These changes were significantly (P=0.04) different. Susceptibility of isolated LDL to copper ion oxidation and plasma levels of malondialdehyde were unchanged during the study. These data suggest that in the postprandial period after a meal rich in used cooking fat, the enzymatic protection of LDL against accumulation of peroxides and atherogenic oxidative modification may be reduced, possibly due to factors associated with apoA1, without acutely affecting the intrinsic resistance of LDL to in vitro oxidation.

Postprandial Cytokine Concentrations and Meal Composition in Obese and Lean Women

The aim of this study was to compare the acute effect of (i) meals rich in saturated fat, oleic acid, and α‐linolenic acid and (ii) meals rich in starch and fiber on markers of inflammation and oxidative stress in obese and lean women. In a crossover study, 15 abdominally obese women (age, 54 ± 9 years; BMI, 37.3 ± 5.5 kg/m2) and 14 lean women (age, 53 ± 10 years; BMI, 22.9 ± 1.9 kg/m2) consumed meals rich in cream (CR), olive oil (OL), canola oil (CAN), potato (POT), and All‐Bran (BRAN) in random order. Blood samples were collected before and up to 6 h after the meals and plasma interleukin‐6 (IL‐6), IL‐8, tumor necrosis factor‐α (TNF‐α), lipid peroxides (LPOs), free‐fatty acids (FFAs), insulin, glucose, and cortisol were measured. Plasma IL‐6 decreased significantly 1 h after the meals then increased significantly above baseline at 4 h and 6 h in obese women and at 6 h in lean women. The incremental area under the curve (iAUC) for IL‐6 was significantly (P = 0.02) higher in obese compared with lean women and was significantly lower following the high fiber BRAN meal compared with a POT meal (P = 0.003). Waist circumference (R = 0.491, P = 0.007) and cortisol AUC (R = −0.415, P = 0.03) were significant determinants of the magnitude of 6 h changes in plasma IL‐6 after the meals. These findings suggest that the postprandial response of plasma IL‐6 concentrations may be influenced by the type of carbohydrate in the meal, central adiposity, and circulating cortisol concentrations in women.

Vitamin E Supplementation and Plasma 8-Isoprostane and Adiponectin in Overweight Subjects

Objective: Isoprostanes are a marker of oxidant stress and atherosclerotic risk, and plasma concentrations are elevated in obesity. Adiponectin is a regulator of insulin sensitivity, and low circulating levels are associated with oxidant stress and obesity. The aim of this study was to determine the effect of vitamin E supplementation on plasma concentrations of 8‐isoprostane and adiponectin in overweight/obese subjects.

HRT does not improve urinary albumin excretion in postmenopausal diabetic women.

The effect of 6 months combined, continuous hormone replacement therapy (HRT) with conjugated equine oestrogen (0.625 mg) and medroxyprogesterone acetate (2.5 mg) on albumin/creatinine ratio (ACR) was determined in postmenopausal diabetic women in a randomised, controlled study. Mean (interquartile range) change in plasma ACR was not (P=0.96) different in women receiving HRT [2 (-11, 21) mg/g, n=20] compared with those randomised to placebo [2 (-1, 14) mg/g, n=27]. Also, the proportion of women with microalbuminuria did not change (P=0.75) during HRT (baseline, 0.45; end of study, 0.53). Furthermore, several risk factors for microalbuminuria including systolic blood pressure (SBP), fasting blood glucose, glycated haemoglobin (HbA1c) and adiposity did not vary significantly during HRT. These data suggest that 6 months HRT does not reverse microalbuminuria caused by prolonged hyperglycaemia and other risk factors that underlie leakage of albumin into the urine in postmenopausal women with type 2 diabetes.

Effect of meals rich in heated olive and safflower oils on oxidation of postprandial serum in healthy men

The present randomised, crossover study sought to determine the effect of meals rich in safflower oil and olive oil (60 g) which had been heated for 8 h at 210 degrees C and the corresponding unheated oils on copper ion oxidation of dilute serum from 16 healthy men. Four hours after the meals rich in the heated oils, there were significant decreases of similar magnitude (-12%) in the lag time in conjugated diene formation during diluted serum oxidation. In the 12 subjects who consumed meals containing unheated oils, the lag time also decreased (-11%) significantly after the meal rich in unheated safflower oil (US) and did not change significantly after the unheated olive oil (UO) meal and these changes were different between the meals at a marginal level of significance (P=0.05). Our data suggest that susceptibility to oxidation of lipoproteins in low antioxidant environments similar to dilute serum may be increased in the postprandial period following meals rich in heat-modified vegetable oils and unheated oils rich in polyunsaturated fatty acids but not following meals rich in native olive oil. These findings may be relevant to the choice of fat to replace saturated fats in lipid-lowering diets and to low risk of coronary heart disease in communities which have a high consumption of olive oil.

Ingestion of native and thermally oxidized polyunsaturated fats acutely increases circulating numbers of endothelial microparticles

Circulating numbers of endothelial microparticles (EMP) are an index of endothelial injury and dysfunction; and microparticles positive to CD31 antibody increase acutely after cooked, fatty fast-food meals that are rich in saturated fatty acids (SAFA) and lipid oxidation products. The aim of this study was to determine the acute effect of meals rich in SAFA and native and thermally oxidized polyunsaturated vegetable oil on circulating numbers of EMP positive to CD144 antibody, a more specific marker of EMP. Twenty-two apparently healthy subjects received isocaloric meals rich in cream (CR), unheated sunflower oil, or heated sunflower oil in a randomized crossover study design. Circulating numbers of CD144-EMP and plasma lipids and Svedberg unit of flotation (S(f)) greater than 400 triglyceride content were measured before and 1 and 3 hours after the meals. Triglycerides in the plasma S(f) greater than 400 fraction increased significantly (P < .001) after the meals, with a significantly (P < .05) larger increase after the CR meal. Plasma CD144-EMP increased significantly (20%, P < .05) after the unheated sunflower oil and heated sunflower oil meals and did not increase significantly (P = .55) after the CR meal. This response was significantly different among the meals (P = .002) when first-visit fasting plasma glucose was a covariate. In conclusion, these data suggest that ingestion of meals rich in n-6 polyunsaturated vegetable oil irrespective of whether it has been mildly thermally oxidized may acutely alter the state of the vascular endothelium, resulting in increased shedding of CD144-EMP. The physiologic implications of these findings remain to be determined.

The effect of rosiglitazone on oxidative stress and insulin resistance in overweight individuals

OBJECTIVE The purpose of this study was to examine the chronic effect of rosiglitazone on oxidative stress, inflammatory markers and hepatic risk factors for type 2 diabetes in overweight individuals. In addition we examined the effect of rosiglitazone on post-glucose challenge levels of glucose and insulin. RESEARCH DESIGN AND METHODS Forty overweight individuals (BMI>27kg/m(2)) were randomized in a double blind fashion to receive 6 months treatment with either rosiglitazone 4mg/day or placebo. Primary endpoints were markers of oxidative stress (plasma peroxides), inflammatory markers (IL-6, TNF-alpha and CRP) and postprandial glucose metabolism (glucose and insulin). Secondary endpoints were changes in insulin resistance as measured by HOMA, first and second phase insulin secretion, adiponectin and effects on lipid and hepatic parameters. RESULTS Plasma peroxides (-15%) decreased significantly during 6 months in the group that received rosiglitazone compared with placebo. Fasting plasma insulin concentrations decreased by 24% and HOMA increased by 35% in those receiving rosiglitazone. Plasma IL-6 (-25%), CRP (-55%) and GGT (-25%) concentrations declined significantly in the rosiglitazone group. Rosiglitazone increased plasma adiponectin by 81%. Treatment with rosiglitazone also resulted in significantly reduced first phase (-33%) and second phase (-20%) insulin release. CONCLUSIONS In overweight non-diabetic people rosiglitazone reduces oxidative stress and improves insulin sensitivity. Rosiglitazone also improves first and second phase insulin secretion and reduces markers of inflammation and GGT.

Serum Protein-Bound 3,4-Dihydroxyphenylalanine and Related Products of Protein Oxidation and Chronic Hemodialysis

Introduction. Protein-bound dihydroxyphenylalanine (PB-DOPA) and its oxidation products are formed by free radical and oxidative attack on proteins. Hemodialysis and uremic toxins can activate leukocytes leading to overproduction of reactive oxygen species such as hydrogen peroxide and hypochlorous acid (HOCl) that increases protein oxidation. Methods. We have used a sensitive fluorometric method to measure PB-DOPA and its oxidation products in proteins after γ-irradiation and incubation with HOCl and in serum from hemodialysis patients and healthy controls. These PB-DOPA concentrations were compared with those measured by HPLC (PB-DOPAHPLC). Results. Fluorescent PB-DOPA increased linearly with increasing amounts of human serum and with increasing amounts of γ-irradiated bovine serum albumin. Concentrations of fluorescent PB-DOPA paralleled PB-DOPAHPLC levels but were approximately 60–70 times higher. Incubation of BSA and human serum albumin (HSA) with HOCl (39.4 mM) significantly (P<0.0001) increased fluorescent PB-DOPA by 5 fold and 10 fold respectively and PB-DOPAHPLC by 6-fold for both proteins. Fluorescent PB-DOPA concentration increased significantly (P<0.0001) by 16-fold in human serum incubated with HOCl (39.4 mM). Mean serum fluorescent PB-DOPA was significantly (P<0.0001) higher in 19 hemodialysis patients (57.7 ± 16.1 µM) compared with 21 healthy controls (33.5 ± 3.7 µM). Mean PB-DOPAHPLC was 4.45 ± 1.63 µM in the healthy controls and 12 hemodialysis patients had values within the range of values in these controls while five patients had values that were outside eight SDs of the mean for healthy subjects. Serum fluorescent PB-DOPA was not correlated significantly with PB-DOPAHPLC in these subjects. Conclusions. The results of this study suggest that fluorophores of the type, which are derived from DOPA can be reproducibly measured in delipidated serum protein and that HOCl can increase levels of these fluorophores-generating proteins and may potentially contribute to the high levels in serum from hemodialysis patients. This high level of fluorescent PB-DOPA compounds is only partially due to authentic PB-DOPA and might also be derived from other related protein oxidation products including those from DOPA oxidation.

IDL Composition and Angiographically Determined Progression of Atherosclerotic Lesions During Simvastatin Therapy

Some patients with coronary artery disease experience continued progression of one or more coronary lesions despite treatment with drugs that inhibit 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and markedly lower plasma cholesterol levels. We examined relationships between the progression of coronary artery lesions and plasma lipoproteins, in particular intermediate density lipoprotein (IDL) and its composition, in 38 patients with coronary artery disease who had been treated with simvastatin for 2 years. Patients were given lipid-lowering dietary advice; 3 months later they were started on simvastatin therapy (10 mg/d) for 1 month, and after review of their plasma cholesterol levels, the dose was increased to 20 mg/d and later to 40 mg/d if the target level of plasma cholesterol had not been attained. Progression of lesions was determined by serial quantitative coronary angiography (variability of 5.5%) and was defined as an increase in percent diameter stenosis (%S)> or =10%; regression was defined as a decrease in %S > or =10%. The proportions of cholesteryl esters (CEs) and free cholesterol decreased significantly (P<.001), and proportions of protein and triglycerides increased significantly (P<.001) in IDL during simvastatin therapy. The CE content of IDL decreased significantly (-7.2 weight [wt]%, n=20, P<.001) in nonprogressors (patients who did not show progression of any lesions) and did not change significantly (-1.8 wt%, n=14, P=.36) in progressors (patients who showed progression of one or more lesions without regression of any lesion). This decrease in IDL CE content in nonprogressors was significantly (P=.01) different compared with the corresponding change in patients classified as progressors. Mean plasma cholesterol concentration tended to increase in progressors (0.47 mmol/L) and tended to decrease in nonprogressors (-0.39 mmol/L) during the initial 3-month diet period, and these changes were significantly different (P=.02). Furthermore, this change in plasma cholesterol level during the initial diet period was correlated significantly with the change in IDL CE content during the entire study (r=.348, n=38, P=.03). These data suggest that IDL CE content may be a determinant of progression of coronary lesions and may be influenced by compliance with or metabolic response to lipid-lowering dietary advice in patients with coronary artery disease during simvastatin treatment.