Increased oxidation resistance of atherogenic plasma lipoproteins at high vitamin E levels in non-vitamin E supplemented men

The oxidative modification of human low density lipoprotein (LDL) has been widely investigated. However, there are no data concerning the oxidation susceptibility of combined very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and low density lipoprotein fraction, although all of them are atherogenic and contain antioxidants such as alpha-tocopherol. We investigated the oxidation susceptibility and oxidation resistance of VLDL + LDL (including IDL) fraction by induction with CuCl2 and its relation to plasma alpha-tocopherol concentration and lipid standardised alpha-tocopherol concentration in 406 non-vitamin E-supplemented men from eastern Finland. Even thought we did not give oral vitamin E or any other antioxidant supplementation to our study participants, we observed a significant, consistent relationship between measurements of oxidation resistance and plasma content of vitamin E. In the multivariate regression model, a high plasma content of vitamin E or lipid standardised vitamin E concentration were the most important determinants of lag time to maximal oxidation rate (standardised regression coefficient = 0.244, P < 0.0001 for vitamin E and 0.211, P < 0.0001 for lipid standardised vitamin E). After statistical adjustment for age, use of cigarettes, hypolipidemic medication (yes vs. no), month of the measurements, plasma concentrations of total ascorbic acid (ascorbic acid + dehydroascorbic acid), beta-carotene and phospholipids, serum concentrations of LDL cholesterol and triglycerides and dietary intake of linoleic acid, the lag time to maximal oxidation rate was 10% (95% C.I. 6.0-13.5%) longer in men in the highest fifth than in the lowest fifth of plasma vitamin E content (P < 0.0001 for trend). When the fifths of lipid standardised vitamin E were compared, the lag time to maximal oxidation rate was 6% (95% C.I. 1.8-10.1%) longer in men in the highest than in the lowest fifth (P < 0.0001 for trend). Our data suggest that alpha-tocopherol is an important antioxidant preventing the in vitro oxidation of VLDL + LDL fraction even in non-supplemented subjects.

Increased risk of non-insulin dependent diabetes mellitus at low plasma vitamin E concentrations: a four year follow up study in men

OBJECTIVE

To investigate whether low vitamin E status is a risk factor for incident non-insulin dependent diabetes mellitus.

DESIGN

Population based follow up study with diabetes assessed at baseline and at four years.

SETTING

Eastern Finland.

SUBJECTS

Random sample of 944 men aged 42-60 who had no diabetes at the baseline examination.

INTERVENTION

Oral glucose tolerance test at four year follow up.

MAIN OUTCOME MEASURES

A man was defined diabetic if he had either (a) a fasting blood glucose concentration > or = 6.7 mmol/l, or (b) a blood glucose concentration > or = 10.0 mmol/l two hours after a glucose load, or (c) a clinical diagnosis of diabetes with either dietary, oral, or insulin treatment.

RESULTS

45 men developed diabetes during the follow up period. In a multivariate logistic regression model including the strongest predictors of diabetes, a low lipid standardised plasma vitamin E (below median) concentration was associated with a 3.9-fold (95% confidence interval 1.8-fold to 8.6-fold) risk of incident diabetes. A decrement of 1 mumol/l of uncategorised unstandardised vitamin E concentration was associated with an increment of 22% in the risk of diabetes when allowing for the strongest other risk factors as well as serum low density lipoprotein cholesterol and triglyceride concentrations.

CONCLUSIONS

There was a strong independent association between low vitamin E status before follow up and an excess risk of diabetes at four years. This supports the theory that free radical stress has a role in the causation of non-insulin dependent diabetes mellitus.

Kuopio Atherosclerosis Prevention Study (KAPS). A population-based primary preventive trial of the effect of LDL lowering on atherosclerotic progression in carotid and femoral arteries

BACKGROUND

The atherosclerotic progression-reducing effect of LDL cholesterol (LDL-C) lowering has been established in subjects with severe atherosclerotic disease but not in persons with elevated LDL cholesterols without severe atherosclerosis. KAPS (Kuopio Atherosclerosis Prevention Study) is the first population-based trial in the primary prevention of carotid and femoral atherosclerosis.

METHODS AND RESULTS

The eligibility requirements were serum LDL-C > or = 4.0 mmol/L and total cholesterol < 7.5 mmol/L. Out of a geographically defined population, 447 men aged 44 to 65 years (mean, 57) were randomized to pravastatin (40 mg/d) or placebo for 3 years. Less than 10% of the subjects had prior myocardial infarction. Thirty-nine men discontinued study medication; however, efficacy data were available for 424 men. The primary outcome was the rate of carotid atherosclerotic progression, measured as the linear slope over annual ultrasound examinations in the average of the maximum carotid intima-media thickness (IMT) of the far wall of up to four arterial segments (the right and left distal common carotid artery and the right and left carotid bulb). For the carotid arteries, at the overall mean baseline IMT of 1.66 mm, the rate of progression of carotid atherosclerosis was 45% (95% CI, 16 to 69%) less in the pravastatin (0.017 mm/y) than the placebo (0.031 mm/y) group (P = .005). In the common carotid artery there was a treatment effect of 66% (95% CI, 30 to 95%; pravastatin 0.010 mm/y; placebo 0.029 mm/y; P < .002) at the overall mean baseline IMT of 1.35 mm. A treatment effect of 30% (95% CI, -1% to 54%) was found for the carotid bulb (pravastatin, 0.028; placebo, 0.040; P = .056) at the overall mean baseline IMT of 2.0 mm. The treatment effect was larger in subjects with higher baseline IMT values, in smokers and in those with low plasma vitamin E levels. There was no significant treatment effect on atherosclerotic progression in the femoral arteries.

CONCLUSIONS

These data establish the antiatherogenic effect of LDL-C lowering by pravastatin in hypercholesterolemic men in a primary prevention setting and suggest a greater effect in smokers than in nonsmokers.

Plasma lipid peroxidation and hyperglycaemia: a connection through hyperinsulinaemia?

Increased lipid peroxidation has been commonly observed in diabetic patients as compared to control subjects. However, studies on the relationship to metabolic control have yielded conflicting results and no data are available on the relationship of hyperinsulinaemia to lipid peroxidation. We investigated, in well-characterized groups of 93 patients with non-insulin-dependent diabetes mellitus, 22 subjects with impaired glucose tolerance (IGT) and 96 subjects with normal glucose tolerance (NGT), the determinants of plasma lipid peroxidation measured by plasma thiobarbituric acid reactive substances (TBARS). These were significantly higher in subjects with IGT (1.04 +/- 0.48 mumol I-1) and in NIDDM patients (1.00 +/- 0.48 mumol I-1) than in those with NGT (0.75 +/- 0.46 mumol I-1; p < 0.05). The glucose tolerance status was the major determinant of increased lipid peroxidation even after controlling for the effects of age, sex, body mass index, physical activity, use of alcohol, smoking, and the use of diuretics. In regression analyses the major determinants of plasma TBARS were fasting plasma glucose, insulin, and apolipoprotein A1 (inversely) levels. To conclude, plasma TBARS were increased in impaired glucose tolerance and in diabetes and they were related to prevailing plasma glucose and insulin levels, suggesting a role for insulin resistance in increased lipid peroxidation process. On the contrary, apolipoprotein A1 may have protective effects in this respect.

Plasma and lipoprotein lipid peroxidation in humans on sunflower and rapeseed oil diets

The effects of natural mixed diets on lipid peroxidation were investigated in humans. In the first study, 59 subjects were fed a rapeseed oil-based diet rich in monounsaturated fatty acids (MUFA) and a sunflower oil-based diet rich in polyunsaturated fatty acids (PUFA) in a cross-over manner for three and a half weeks. The lipid peroxidation products in plasma were determined by measuring conjugated dienes and malondialdehyde (MDA). In a second study, plasma thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides, and the susceptibility of very low density lipoprotein+low-density lipoprotein (LDL) to in vitro oxidation were measured from subjects fed similar MUFA and PUFA diets for six weeks diets. No significant differences in plasma MDA or conjugated diene concentrations were found after the rapeseed oil diet or the sunflower oil diet in Study 1. In the second study, a small but significant decrease (P < 0.05) in both lipid hydroperoxides and TBARS was observed in the LDL fraction after the sunflower oil diet. The in vitro oxidation gave opposite results, showing increased oxidation after the sunflower oil diet. Despite a high intake of alpha-tocopherol during the oil periods, no increase in plasma alpha-tocopherol was noticed in either study. The results suggest that moderate changes in the fatty acid composition in the Western-type diet may be adequate to affect lipoprotein susceptibility to oxidation in vitro, but there is considerable disparity with some indices of in vivo lipid peroxidation.

Lowering of body iron stores by blood letting and oxidation resistance of serum lipoproteins: a randomized cross-over trial in male smokers

OBJECTIVES

The purpose of this study was to test the hypothesis that the reduction of body iron stores by venesection (blood letting) would reduce the susceptibility to oxidation of atherogenic serum lipoproteins.

DESIGN

This is a randomized, controlled cross-over trial in 14 regularly smoking men with elevated serum ferritin concentration. The study design comprised two 14-week study periods, with a 14-week wash-out period in between, with either blood donations or control.

SETTING

The study site was the Research Institute of Public Health, University of Kuopio. Investigators from the Division of Epidemiology, University of Minnesota, Minneapolis, participated in the planning of the study.

SUBJECTS

Fourteen volunteers who were heavy smokers and had previous experience in blood letting were recruited for the study.

INTERVENTIONS

During the intervention periods, the subjects donated 450 mg (500 mL) of blood three times in 14 weeks.

MAIN OUTCOME MEASUREMENTS

Oxidation resistance of very low density lipoprotein (VLDL)/low density lipoprotein (LDL) was measured after inducing oxidation with haemin and H2O2.

RESULTS

Serum ferritin concentration was reduced by 44% [95% confidence interval (CI) 8-82%, P = 0.021] during the venesection periods, the maximal oxidation velocity was decreased by 20% (95% CI 3-30%, P = 0.032), and the lag time to start of oxidation was lengthened (oxidation resistance increased) by 33% (95% CI 1-64%, P = 0.036).

CONCLUSIONS

These observations indicate that the reduction of body iron stores by venesection can increase the oxidation resistance of serum VLDL/LDL in regularly smoking men.

Intake of mercury from fish, lipid peroxidation, and the risk of myocardial infarction and coronary, cardiovascular, and any death in eastern Finnish men

BACKGROUND

Even though previous studies have suggested an association between high fish intake and reduced coronary heart disease (CHD) mortality, men in Eastern Finland, who have a high fish intake, have an exceptionally high CHD mortality. We hypothesized that this paradox could be in part explained by high mercury content in fish.

METHODS AND RESULTS

We studied the relation of the dietary intake of fish and mercury, as well as hair content and urinary excretion of mercury, to the risk of acute myocardial infarction (AMI) and death from CHD, cardiovascular disease (CVD), and any cause in 1833 men aged 42 to 60 years who were free of clinical CHD, stroke, claudication, and cancer. Of these, 73 experienced an AMI in 2 to 7 years. Of the 78 decreased men, 18 died of CHD and 24 died of CVD. Men who had consumed local nonfatty fish species had elevated hair mercury contents. In Cox models with the major cardiovascular risk factors as covariates, dietary intakes of fish and mercury were associated with significantly increased risk of AMI and death from CHD, CVD, and any death. Men in the highest tertile (> or = 2.0 micrograms/g) of hair mercury content had a 2.0-fold (95% confidence interval, 1.2 to 3.1; P = .005) age- and CHD-adjusted risk of AMI and a 2.9-fold (95% CI, 1.2 to 6.6; P = .014) adjusted risk of cardiovascular death compared with those with a lower hair mercury content. In a nested case-control subsample, the 24-hour urinary mercury excretion had a significant (P = .042) independent association with the risk of AMI. Both the hair and urinary mercury associated significantly with titers of immune complexes containing oxidized LDL.

CONCLUSIONS

These data suggest that a high intake of mercury from nonfatty freshwater fish and the consequent accumulation of mercury in the body are associated with an excess risk of AMI as well as death from CHD, CVD, and any cause in Eastern Finnish men and this increased risk may be due to the promotion of lipid peroxidation by mercury.

Increase in oxidation resistance of atherogenic serum lipoproteins following antioxidant supplementation: a randomized double-blind placebo-controlled clinical trial

OBJECTIVE

To test the effect of supplementation of diet with ascorbic acid, selenium, alpha-tocopherol and beta-carotene on the oxidation resistance of very low (VLDL) + low density lipoprotein (LDL).

DESIGN

A randomized placebo-controlled double-masked clinical trial.

SETTING

In healthy men aged 30-58 years smoking regularly 15-40 cigarettes/day.

SUBJECTS

Forty subjects recruited from the general population, who all completed the study.

INTERVENTION

400 mg of slow release ascorbic acid, 100 micrograms of organic selenium, 200 mg of D-alpha-tocopheryl acetate and 30 mg of beta-carotene daily or placebo, 20 men in each group for 3 months.

MAIN OUTCOME MEASURES

The oxidation resistance of VLDL + LDL measured by inducing oxidation with copper chloride and, separately, with a combination of haemin and H2O2.

RESULTS

In plasma, alpha-tocopherol increased by 72%, beta-carotene by 209%, ascorbate by 45% and selenium by 20% in the supplemented men. The lag time to oxidation increased by 27% [95% confidence interval (CI) 18-35%, P < 0.001] after copper and by 29% (95% CI 12-46%, P = 0.002) after haemin plus H2O2 in the supplemented group as compared to the placebo group by t-tests. The respective net changes in the maximal oxidation velocity were a reduction of 10% (95% CI 1-21%, P = 0.037) after copper and a reduction of 15% (95% CI-1 to 30%, P = 0.070) after haemin and H2O2.

CONCLUSIONS

These findings provide further confirmation for the notion that the supplementation of diet with antioxidative vitamins and selenium increases the oxidation resistance of atherogenic lipoproteins in human plasma.

Higher levels of conditioning leisure time physical activity are associated with reduced levels of stored iron in Finnish men

The authors investigated the association of the amount and intensity of conditioning leisure time physical activity with serum ferritin and blood hemoglobin concentrations in 1,743 eastern Finnish men who were aged 42-60 years during the period 1984-1989. The duration and frequency of physical activity were associated inversely with serum ferritin (p = 0.003 for duration and p < 0.001 for frequency) and blood hemoglobin (p = 0.002 for duration and p = 0.019 for frequency) in multivariate regression models, after adjustment for major confounders. Men in the highest quartile of duration (> 2.6 hours/week) had a 16.8% lower mean serum ferritin concentration and men in the highest category of frequency (> 3 sessions/week) had a 19.9% lower mean serum ferritin concentration than men with a low duration (< 0.4 hour/week) and frequency (< 1 session/week), respectively. For blood hemoglobin, the respective differences were 1.3% and 1.0%. The intensity of physical activity was significantly associated only with blood hemoglobin (p = 0.011). Together with the authors' previous finding concerning the association between high serum ferritin and an excess risk of acute myocardial infarction, these data suggest that a reduction in stored iron levels could be one mechanism through which conditioning leisure time physical activity decreases the risk of coronary heart disease.

Effects of two low-fat diets, high and low in polyunsaturated fatty acids, on plasma lipid peroxides and serum vitamin E levels in free-living hypercholesterolaemic men

Diet enriched with polyunsaturated fat may increase the susceptibility of LDL to oxidation. Therefore the effects of two low-fat diets on plasma lipid peroxides in free-living mildly hypercholesterolaemic men (n = 37) were investigated in a randomized single-blind 28-week study. Composition of the diets were (1) American Heart Association (AHA) type 32/10:8:8 (indicating percentages of energy from total fat/saturated fat:monoenes:polyenes in actual diet); (2) low-fat 30/12:8:3. The subjects kept 3-day dietary records five times during the study to estimate the intake of nutrients. Plasma lipid peroxides were measured photometrically as the thiobarbituric-acid reactive substances (TBARS). Levels of serum vitamin E during the study were also determined. Mean change (+/- SD) in serum low density lipoprotein (LDL) cholesterol was similar in both groups (-0.32 +/- 0.76 vs -0.32 +/- 0.87 mmol/l) (AHA type vs low-fat). Level of TBARS decreased (P < 0.05) during the AHA type diet (-8.4 +/- 37.1%) (mean +/- SD) and increased (P = 0.228) during the low-fat diet (+8.7 +/- 27.0%) from 0 to 6 months. The mean intake of total active tocopherols was greater (14.7 +/- 3.7 mg) during the AHA type diet compared to the low-fat diet (7.8 +/- 2.1 mg). Serum vitamin E to LDL cholesterol ratio increased from 8.9 +/- 2.9 to 9.6 +/- 2.4 nmol/mmol (0 vs 6 months) (P = 0.07) during the AHA type diet and from 8.6 +/- 2.6 to 9.3 +/- 2.4 nmol/mmol (P = 0.159) during the low-fat diet.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance liquid chromatographic assay of platelet-produced thromboxane B2

A method for the routine determination of platelet-produced thromboxane B2 (TXB2) from human serum is presented. To induce the secretion of thromboxane A2 from the platelets, blood is kept at 37 degrees C for 30 min before serum is separated. Serum is prepurified through small reversed-phase columns and TXB2 is analysed by reversed-phase high-performance liquid chromatography. A column-switching technique is used to remove the interfering compounds present in serum. The detection limit with standard solution is 30 ng per injection. The method was applied to the measurement of platelet-produced TXB2 serum from 1040 men. The mean TXB2 was 247 +/- 134 ng/ml in the serum of men who had not used prostaglandin inhibitors, and 208 +/- 123 ng/ml in the serum of men who had used a prostaglandin inhibitor during a two-week period before blood sampling.

High stored iron levels are associated with excess risk of myocardial infarction in eastern Finnish men

BACKGROUND

Iron can induce lipid peroxidation in vitro and in vivo in humans and has promoted ischemic myocardial injury in experimental animals. We tested the hypothesis that high serum ferritin concentration and high dietary iron intake are associated with an excess risk of acute myocardial infarction.

METHODS AND RESULTS

Randomly selected men (n = 1,931), aged 42, 48, 54, or 60 years, who had no symptomatic coronary heart disease at entry, were examined in the Kuopio Ischaemic Heart Disease Risk Factor Study (KIHD) in Eastern Finland between 1984 and 1989. Fifty-one of these men experienced an acute myocardial infarction during an average follow-up of 3 years. On the basis of a Cox proportional hazards model adjusting for age, examination year, cigarette pack-years, ischemic ECG in exercise test, maximal oxygen uptake, systolic blood pressure, blood glucose, serum copper, blood leukocyte count, and serum high density lipoprotein cholesterol, apolipoprotein B, and triglyceride concentrations, men with serum ferritin greater than or equal to 200 micrograms/l had a 2.2-fold (95% CI, 1.2-4.0; p less than 0.01) risk factor-adjusted risk of acute myocardial infarction compared with men with a lower serum ferritin. An elevated serum ferritin was a strong risk factor for acute myocardial infarction in all multivariate models. This association was stronger in men with serum low density lipoprotein cholesterol concentration of 5.0 mmol/l (193 mg/dl) or more than in others. Also, dietary iron intake had a significant association with the disease risk in a Cox model with the same covariates.

CONCLUSIONS

Our data suggest that a high stored iron level, as assessed by elevated serum ferritin concentration, is a risk factor for coronary heart disease.

Autoantibody against oxidised LDL and progression of carotid atherosclerosis

Oxidative modification of LDL renders it immunogenic and autoantibodies to epitopes of oxidised LDL, such as malondialdehyde (MDA)-lysine, are found in serum and recognise material in atheromatous tissue. However, there has been no prospective study to assess the importance of oxidised LDL among patients with vascular disease. We compared the titre of autoantibodies to MDA-modified LDL and native LDL in baseline serum samples of 30 eastern Finnish men with accelerated two-year progression of carotid atherosclerosis and 30 age-matched controls without progression. Neither group had specific antibody binding to native LDL. A titre was defined as a ratio of antibody binding to MDA-LDL/binding to native LDL. Cases had a significantly higher titre to MDA-LDL (2.67 vs 2.06, p = 0.003). Cases also had a greater proportion of smokers (37% vs 3%), higher LDL cholesterol (4.2 mmol/l vs 3.6 mmol/l), and higher serum copper concentration (1.14 mg/l vs 1.04 mg/l). Even after adjusting for these variables and the severity of baseline atherosclerosis, the difference in antibody titre remained significant in a multifactorial logistic model (p = 0.031). Thus, the titre of autoantibodies to MDA-LDL was an independent predictor of the progression of carotid atherosclerosis in these Finnish men. Our data provide further support for a role of oxidatively modified LDL in atherogenesis.

Comparison of gel permeation chromatography, density gradient ultracentrifugation and precipitation methods for quantitation of very-low-, low- and high-density lipoprotein cholesterol

Human VLDL, LDL and HDL (very-low-, low-, and high-density lipoproteins) were isolated from plasma by gel permeation chromatography with one pre-ultracentrifugation step. The column effluent was monitored at 280 nm. The cholesterol content of the fractions correlated well with fractions from sequential ultracentrifugation (VLDL, r = 0.839; LDL, r = 0.924; HDL, r = 0.766) or precipitation (LDL, r = 0.975; HDL, r = 0.972) methods. The average triglyceride, phospholipid and protein compositions of the separated lipoprotein fractions were close to those of the ultracentrifugally isolated fractions reported previously. Apolipoproteins A1 and B were determined from fractions to confirm the right distribution between different lipoproteins.

Plasma catecholamines: laboratory aspects

In this review the methods used for analysis of plasma catecholamines in clinical chemical laboratories are discussed. The physiology of catecholamines as well as their measuring indications are discussed, together with concise evaluation of the methods most commonly used, namely indirect radioenzymatic assays or direct determinations by high-performance liquid chromatography combined with either electrochemical or fluorometric detection. The main advantage of radioenzymatic assay is its sensitivity and thus the need for only a small sample. Liquid chromatographic methods in general are less tedious, relatively rapid, and cheap, and omit the use of radionuclides. Both of these methods, however, are subject to a number of analytical errors, which can only be avoided by proper development of methods and skilled use of these methods. Little routine work is done using either radioimmunoassay or gas-chromatography.

Plasma haemoglobin determination using chlorpromazine as a non-carcinogenic reagent

Plasma haemoglobin was assayed with the non-carcinogenic reagent phenothiazine. This method is sensitive and allows the measurement of plasma haemoglobin concentrations in the range 4-500 mg/l with a within-run CV of 2.1%, and a between-run CV of 4.3%. A spectrophotometric scanning method (x) based on the determination of haemoglobin as haemiglobin cyanide using the Soret band at 419 nm correlated well with the phenothiazine method (y): y = 1.07x + 15.8, r = 0.995, n = 31. It was found that the absorbances in the phenothiazine method were markedly dependent on the concentration of phosphoric acid.

Quantitative changes in aminoacylation of transfer RNA and in free amino acids during fructose-induced depletion of adenine nucleotides in rat liver

Fructose induces depletion of adenine nucleotides in liver and also strongly inhibits incorporation of radioactive amino acids into protein (Mäenpää, P.H., Raivio, K.O. and Kekomäki, M.P. (1968) Science 161, 1253-1254). In this study we have investigated the effects of fructose on aminoacylation of tRNA and on free amino acids in rat liver. 30 min after D-fructose (30 mmol/kg) was injected intraperitoneally into rats, liver ATP was reduced by 58%, ADP by 42%, AMP by 13%, the ATP/ADP ratio by 30%, and total adenine nucleotides by 48%. Using gas chromatography, the aminoacylation of tRNA was determined by quantifying the endogenous amino acids attached to tRNA in vivo. Aminoacylation was reduced by 31%. With different amino acids, reduction varied from 4% (asparagine plus aspartic acid) to 58% (arginine). On the other hand, the amount of free amino acids in the liver was increased by 24%. The most marked individual change was in alanine, which increased 5.7-times. This may have resulted from a combination of effects involving an increased production of alanine in muscle and liver and decreased hepatic gluconeogenesis from alanine caused by the ATP depletion.