Plasma lipid peroxides: relationships to cardiovascular risk factors and prevalent cardiovascular disease.

BACKGROUND: The epidemiology of plasma lipid peroxides, which may play a role in atherogenesis, has not been well defined. AIM: To study the relationships of plasma lipid peroxides to cardiovascular risk factors in a random population sample. DESIGN: Random, age- and sex-stratified population sample. METHODS: We studied 739 men and women aged 25-74 years. Lipid peroxides were assayed by the thiobarbituric acid (TBA) assay for malondialdehyde (MDA) in stored plasma samples. RESULTS: Lipid peroxide levels increased with age. In men, lipid peroxides were significantly associated with smoking habit. Lipid peroxides correlated with non-fasting serum triglycerides (r = 0.33; p < 0.0001) in both sexes. Weaker associations were observed for cholesterol, high-density lipoprotein cholesterol (inversely), body mass index, fibrinogen and white cell count; as well as an inverse association with serum vitamin C in men. DISCUSSION: These findings clarify the relationships of plasma lipid peroxides to cardiovascular risk factors; and are consistent with the hypothesis that lipid peroxidation may be one mechanism through which several risk factors may promote cardiovascular disease.

Improving the quality of near-patient blood glucose measurement.

The quality of near-patient blood glucose measurement was audited in our hospitals in 1990, when a diversity of glucose meters were in use, by sending three samples of unknown (to the meter user) concentration to each user and collecting and analysing the results produced. The overall performance was unsatisfactory with a mean coefficient of variation (CV) of 23.5%. A scheme involving training, quality control and external quality assurance was introduced in 1993 based on the Bayer Glucometer II meter. This meter was used exclusively throughout our hospitals. Data from the quality assurance scheme showed that the overall CV fell initially to 14-16% and then settled at about 10-12% for the following 2 years. Unacceptable results (those more than two standard deviations from the mean) were 8-12% of the total. A new meter was introduced in 1995 (the Bayer Glucometer 4) which had the advantages of 'no-wipe' and automatic timing technology and in the subsequent year overall CV fell to 5-6% and has remained at this level. The frequency of unacceptable results fell to 5-7%. The improved precision figures encouraged us to change criteria for acceptability to mean +/- 15%. Using these criteria the level of unacceptable results is now 1-2%. This study shows that introducing training, quality control procedures, a quality assurance scheme and improved meter technology all backed by laboratory expertise can produce significant improvement in the quality of near patient blood glucose measurement.

The effect of haemolysis on blood glucose meter measurement.

A study was performed to assess the effect of varying degrees of sample haemolysis on the measurement of blood glucose by the Accutrend, Companion 2, ExacTech, Glucometer II, Glucometer 4, One Touch II, and Reflolux II blood glucose meters. Fresh venous blood was sonicated to induce complete haemolysis and then added in increasing proportions to homologous untreated blood to obtain nine samples with free haemoglobin concentrations up to 50 g l-1. The Accutrend meter showed the only significant (p < 0.05) linear relationship to degree of haemolysis (r = 0.988, p < 0.0001). For every 7% of red cells lysed, the Accutrend value increased by 15%. All other meters gave results which were within 15% of the non-haemolysed value. However, extreme (100%) haemolysis not only affected the Accutrend (glucose value 108% greater than reference) but also the ExacTech (+98%), the Glucometer II (-32%), and the Companion 2 (-41%). Thus, unwitting use of a haemolysed sample to measure whole blood glucose may, with the Accutrend in particular, lead to erroneous results.

Glycated haemoglobin values: problems in assessing blood glucose control in diabetes mellitus.

OBJECTIVE: To see whether two measures of glycated haemoglobin concentration--the haemoglobin A1 (HbA1) value and the haemoglobin A1c (HbA1c) value--assess blood glucose control differently in diabetes. DESIGN: Diabetic patients had glycaemic control assessed on the basis of HbA1 and HbA1c values measured by the same high performance liquid chromatography instrument and on the basis of HbA1 measured by electrophoresis. SETTING: A diabetic outpatient clinic. SUBJECTS: 208 diabetic patients and 106 non-diabetic controls. MAIN OUTCOME MEASURES: Glycated haemoglobin concentrations classified according to European guidelines as representing good, borderline, or poor glycaemic control by using standard deviations from a reference mean. RESULTS: Fewer patients were in good control (25;12%) and more poorly controlled (157;75%) as assessed by the HbA1c value compared with both HbA1 assays (39 (19%) and 130 (63%) respectively when using high performance liquid chromatography; 63 (30%) and 74 (36%) when using electrophoresis). The median patient value was 8.0 SD from the reference mean when using HbA1c, 5.9 when using HbA1 measured by the same high performance liquid chromatography method, and 4.1 when using HbA1 measured by electrophoresis. CONCLUSIONS: Large differences exist between HbA1 and HbA1c in the classification of glycaemic control in diabetic patients. The HbA1c value may suggest a patient is at a high risk of long term diabetic complications when the HbA1 value may not. Better standardisation of glycated haemoglobin measurements is advisable.

Variations in sample pH and pO2 affect ExacTech meter glucose measurements.

A study was conducted to assess the effect of changes in sample pH and pO2 on the Accutrend, ExacTech Companion, Glucometer II, One Touch II, and Refloflux II blood glucose meters. Venous blood was tonometered after the addition of strong acid or alkali to produce 10 samples with a pH range of 6.54 to 7.73 but with a similar mean pO2 (9.09 +/- 0.096 (SEM) kPa) and pCO2 (5.52 +/- 0.024 kPa). The ExacTech showed a > 15% deviation from the value obtained at pH 7.40 below pH 6.95 and above pH 7.85 (r = 0.69, p = 0.026). Ten further samples were made with a pO2 range of 2.0 to 33.6 kPa but mean pH (7.28 +/- 0.012) and pCO2 (7.98 +/- 0.25 kPa) kept alike. The ExacTech was accurate at pO2 = 11.5 kPa but deviated by > 15% below pO2 = 5.8 kPa and above 22.9 kPa (r = -0.95, p = 0.00002). The Accutrend and One Touch II required a pO2 change of 42 and 45 kPa to achieve the same error (r = -0.82 and r = -0.67 respectively). Thus caution is required in the interpretation of ExacTech glucose measurements in severely acidotic or hypoxic patients.

A ward comparison between the One Touch II and Glucometer II blood glucose meters.

A 6-week clinical evaluation of the One Touch II blood glucose meter was performed in a medical ward specializing in diabetic patients and compared to the existing Glucometer II system. Nursing staff trained in both methods performed 267 capillary blood glucose measurements using the two meters. A reference capillary blood glucose was performed simultaneously on 129 of these occasions using a Yellow Springs Instrument analyser. The One Touch II correlated better with the reference (r = 0.97) than the Glucometer II (r = 0.86) and was equally close or closer to the Yellow Springs Instrument on 82% of occasions. A greater proportion of samples measured by the One Touch II were within 15% of the reference value (83% vs 66%). There were also 17 cases where the One Touch II was able to give a measurement which was outwith the analytical range of the Glucometer II. A questionnaire revealed the nursing staff unanimously preferred using the One Touch II to their present meter. It is concluded that in a ward setting the One Touch II meter showed improved accuracy, usefulness in its wider analytical range, and a greater user preference in comparison to the Glucometer II.

Evaluation of glycaemic control limits using the Ames DCA 2000 HbA1c analyser.

The Ames DCA 2000 is a benchtop analyser that measures HbA1c by an agglutination inhibition immunoassay using a monoclonal antibody. Laboratory and nursing staff measured HbA1c on-site in 78 patients with Type 1 diabetes at the outpatient clinic. Significant correlations were noted with both the Corning Glytrac total HbA1 assay (r = 0.89) and the Novoclone assay for HbA1c (r = 0.95). Mean within-assay CV was 1.6% and 3.0% at HbA1c of 5.4% and 13.0%, respectively, while between-assay CVs were 4.2% and 3.8%. These results are as good as our routine laboratory method based on the Corning HbA1 assay. Locally derived reference population data for HbA1c were produced and patients were assigned to categories of good, acceptable, and poor glycaemic control using conventional recommendations for Type 2 diabetes. There was poor agreement between the methods, with only 22% of patients achieving good/acceptable control using the DCA 2000, while 46% of patients had an HbA1 in this range. It appears that the convention for derivation of control limits for HbA1 does not hold for this HbA1c assay.

Smoking, haemostatic factors and lipid peroxides in a population case control study of peripheral arterial disease.

The aim of this study was to determine differences between cases of peripheral arterial disease and healthy controls in levels of haemostatic factors and lipid peroxides and the influence of cigarette smoking. The study groups were selected from the Edinburgh Artery Study which is a random sample survey of men and women aged 55-74 years. Mean levels of plasma fibrinogen, von Willebrand factor, beta-thromboglobulin, plasminogen activator inhibitor (type I), cross-linked fibrin degradation products and lipid peroxides were markedly elevated in 121 study cases compared with 126 age- and sex-matched controls. For example, cross-linked fibrin degradation products had a geometric mean of 106.8 ng/ml (95% confidence interval (CI) 95.3, 119.8) in study cases and 74.7 ng/ml (95% CI 67.0, 83.4) in controls (P < 0.001). Inclusion of smoking in logistic regressions of each factor on peripheral arterial disease significantly reduced the odds of disease for von Willebrand factor and for cross-linked fibrin degradation products, but had little effect on the increased odds associated with fibrinogen, beta-thromboglobulin, plasminogen activator inhibitor and lipid peroxides. We conclude that, in men and women in Edinburgh, peripheral atherosclerosis is associated with lipid peroxidation, endothelial disturbance, platelet activation, elevated fibrinogen, fibrin formation and increased inhibition of fibrinolysis. The most important effects of cigarette smoking in promoting atherosclerosis may be endothelial disturbance and fibrin formation.

A comparison of different methods of assessing free radical activity in type 2 diabetes and peripheral vascular disease.

Increased free radical activity in diabetes mellitus may contribute to the higher prevalence and mortality from macrovascular disease in diabetic patients. To investigate this, levels of plasma antioxidants (superoxide dismutase, caeruloplasmin, plasma, and lysate thiol), diene conjugates, lipid peroxides, and chemiluminescence were measured in diabetic and non-diabetic patients with peripheral vascular disease compared with healthy control subjects. Caeruloplasmin, diene conjugate ratio, and lipid peroxides were significantly increased in patients with vascular disease but there was no difference between diabetic and non-diabetic patients. Conjugated diene ratio correlated with caeruloplasmin (r = 0.40, p < 0.02) and inversely with superoxide dismutase level (r = 0.36, p < 0.05) but there was no significant correlation between other antioxidants and diene conjugates, lipid peroxides or chemiluminescence. The relationship between different indirect measurements of free radical activity is variable but there appears to be no additive effect of diabetes on the increased free radical activity associated with vascular disease.

Probucol reduces plasma lipid peroxides in man.

Although primarily used as a lipid lowering drug, probucol also possesses anti-oxidant activity and has been shown in animal models to inhibit or delay the progression of atherosclerosis. It has been suggested that this anti-atherosclerotic effect may occur through inhibition of free radical oxidation of low density lipoprotein. The aim of this study was to investigate the effects of probucol on free radical activity in hyperlipidaemic patients. Plasma lipid peroxides were measured before probucol treatment, at 4 and 12 weeks treatment and then 4 weeks after stopping probucol. Lipid peroxide concentrations were significantly reduced during and 4 weeks after stopping treatment with probucol, when compared with baseline values. There were no changes in plasma vitamin E concentrations. The results of this study indicate that probucol reduces lipid peroxidation in patients, an effect which may occur through a free radical scavenging action.

Free radical activity and hemostatic factors in NIDDM patients with and without microalbuminuria.

In non-insulin-dependent diabetes mellitus (NIDDM) patients, microalbuminuria predicts early mortality, predominantly from cardiovascular disease. Increased free radical activity and abnormalities in hemostasis have been implicated in the development of vascular disease. Therefore, we measured markers of free radical activity (nonperoxide-conjugated diene isomer of linoleic acid [PL-9,11-LA'] and lipid peroxides expressed as malondialdehyde [MDA]) along with the hemostatic variables: fibrinogen, von Willebrand factor (vWf), plasminogen activator inhibitor (PAI-1), tissue plasminogen activator (t-PA), and plasmin activity (B beta 15-42) in 24 NIDDM patients (12 patients with microalbuminuria and 12 without microalbuminuria) and in 12 age-matched control subjects. There were no differences in linoleic acid (PL-9,12-LA) concentrations between the three groups. PL-9,11-LA' was elevated in the microalbuminuric patients compared with control subjects (P less than 0.05), but there was no difference between the two diabetic groups. MDA was elevated in the microalbuminuric diabetic patients compared with those patients without microalbuminuria (P less than 0.05) and control subjects (P less than 0.001). MDA was also increased in the patients without microalbuminuria compared with control subjects (P less than 0.01). Except for B beta 15-42, all the hemostatic variables were increased (P less than 0.05) in the diabetic patients compared with control subjects. The microalbuminuric diabetic patients had further increases in vWf (P less than 0.03) and t-PA (P less than 0.03) compared with patients with microalbuminuria. Our study suggests that there is an increase in free radical activity and abnormalities in hemostatic variables favoring a hypercoagulable state in NIDDM, especially in those with microalbuminuria.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary venous lipid peroxide concentrations after coronary angioplasty: correlation with biochemical and electrocardiographic evidence of myocardial ischaemia.

BACKGROUND: Raised lipid peroxide concentrations in coronary venous plasma have been reported after coronary angioplasty in humans. This may reflect increased free radical activity after myocardial ischaemia and reperfusion. If so, it may be possible to correlate lipid peroxide concentrations with the degree of myocardial ischaemia produced during angioplasty. METHODS: 15 patients (age range 42-70; 12 men) with stable angina pectoris undergoing angioplasty of a proximal left anterior descending coronary artery stenosis were studied. Plasma lipid peroxide and lactate concentrations were measured in sequential blood samples taken from the great cardiac vein before and immediately after one to five serial 60 second balloon inflations. The maximum ST segment shift during each balloon inflation was also measured. RESULTS: Lipid peroxide concentrations in coronary venous plasma were raised from pre-angioplasty values by more than 2 SDs of the relevant measurement error after 27 out of 46 (59%) balloon inflations. Lactate concentrations were raised after 43 out of 46 (93%) balloon inflations. No significant difference was found between the peak percentage change of either lipid peroxide or lactate concentrations after any of the first three serial inflations. The maximum ST segment shift after each of the first three serial inflations was also similar. Coronary venous lactate concentrations after balloon inflation correlated positively with the maximum ST segment shift, but did not correlate with lipid peroxide concentrations. CONCLUSIONS: Raised lipid peroxide concentrations in coronary venous plasma can be detected in humans after balloon angioplasty. There is no positive correlation between lipid peroxide concentrations in coronary venous plasma after angioplasty and the degree of preceding myocardial ischaemia as assessed by either ST segment shift or lactate production. These indices showed that one to three serial 60 second balloon inflations each produce a similar degree of myocardial ischaemia. The origin of the raised lipid peroxide concentrations in coronary venous plasma after angioplasty remains unknown.

Within-clinic glycosylated haemoglobin measurement.

The performance of the Diamat HPLC analyser (Bio Rad Instruments) was assessed, and the effect of this on-site HbA1 assay on the therapeutic decisions made at the diabetic clinic evaluated. The intra-assay CV for HbA1 at concentrations of 8.3 and 13.4% was 3.8 and 0.4%, respectively, with inter-assay CV of 5.0 and 3.0%. On a single day 82 HbA1 tests on consecutive patients were performed at the clinic. In 43 insulin-treated patients and 79 non-insulin-treated diabetic patients the HbA1 result changed the management decision in 25 and 18% of patients, respectively. The relationship between HbA1 and self blood glucose monitoring (SBGM) results in the previous 6-week period were also evaluated. In 41% of patients with insulin-treated diabetes who produced SBGM diaries there was a discrepancy between categories of blood glucose control, all of these patients having better SBGM than HbA1 values. This study highlights the feasibility and value of a within-clinic HbA1 assay for clinical decision-making and its usefulness in identifying problems of agreement with self-monitored tests.

Effect of marathon training on the plasma lactate response to submaximal exercise in middle-aged men.

Twenty-one previously sedentary male volunteers (aged 35-50 years) undertook a defined marathon training programme lasting 30 weeks. At weeks 0 (T1), 15 (T2) and 30 (T3) they underwent measurement of maximal oxygen uptake (VO2 max), submaximal VO2 and submaximal plasma lactate concentration during cycle ergometry. No exercise was taken for 24-48 hours prior to testing. During training aerobic power increased significantly (p less than 0.001) from an initial VO2 max at T1 of 33.9 +/- 6 (mean +/- sd) ml.kg-1min-1 to 39 +/- 5.6 ml.kg-1min-1 at T2 but the T3 value of 39.2 +/- 5.2 ml.kg-1min-1 was not significantly different from that at T2. Plasma lactate concentration of 4 mmol.l-1 (OBLAw) occurred at a significantly (P less than 0.05) higher workload (155 +/- 28 w) at T2 compared with T1 (132 +/- 30 w) but the T3 figure was 137 +/- 34 w. OBLA VO2 at T1 was 2.04 +/- 0.42 l.min-1, at T2 was 2.24 +/- 0.04 l.min-1 but at T3 was 2.03 +/- 0.30 l.min-1 (T1:T2 P less than 0.05, T1:T3 NS). OBLA % VO2 max at T1 was 75 +/- 12%, at T2 was 73 +/- 11% but at T3 was 62 +/- 10% (T1:T2 NS, T1:T3 P less than 0.01).

Serum lactate dehydrogenase and creatine kinase during marathon training.

Serum total creatine kinase (CK) and the lactate dehydrogenase (LDH) isoenzymes were studied in 38 sedentary middle-aged men (aged 35-50 yrs) during a 30 week marathon training programme. Basal CK activity rose by 33% after 15 weeks but a significant rise (27%) in LDH activity took 30 weeks to occur. Post-exercise (maximum test on a bicycle ergometer) CK and LDH activities were higher than pre-exercise levels but the increment in enzyme activity following exercise did not change. LDH1 and LDH2 isoenzyme activity increased by 2.5% and 4% of total LDH respectively while LDH3 and LDH5 decreased by 3.9% and 2.4% respectively over 30 weeks. Post marathon total CK did not correlate with finishing time at 30 mins or 30 hrs post race. The range of CK MB isoenzyme activity at 30 mins post race was 1.8-9.8% of total CK with 11 subjects having a value above 6%. The training programme appears not to have affected muscle CK and LDH release during exercise but isoenzyme distribution changes reflect the adaptations known to occur in muscle during endurance training. Unfortunately only 16 subjects were available for all the investigations, and it is these upon whom most of the data were obtained.