On the antioxidant properties of erythropoietin and its association with the oxidative-nitrosative stress response to hypoxia in humans

AIM

The aim of this study was to examine if erythropoietin (EPO) has the potential to act as a biological antioxidant and determine the underlying mechanisms.

METHODS

The rate at which its recombinant form (rHuEPO) reacts with hydroxyl (HO˙), 2,2-diphenyl-1-picrylhydrazyl (DPPH˙) and peroxyl (ROO˙) radicals was evaluated in-vitro. The relationship between the erythopoietic and oxidative-nitrosative stress response to poikilocapneic hypoxia was determined separately in-vivo by sampling arterial blood from eleven males in normoxia and following 12 h exposure to 13% oxygen. Electron paramagnetic resonance spectroscopy, ELISA and ozone-based chemiluminescence were employed for direct detection of ascorbate (A(˙-) ) and N-tert-butyl-α-phenylnitrone spin-trapped alkoxyl (PBN-OR) radicals, 3-nitrotyrosine (3-NT) and nitrite (NO2-).

RESULTS

We found rHuEPO to be a potent scavenger of HO˙ (kr = 1.03-1.66 × 10(11) m(-1) s(-1) ) with the capacity to inhibit Fenton chemistry through catalytic iron chelation. Its ability to scavenge DPPH˙ and ROO˙ was also superior compared to other more conventional antioxidants. Hypoxia was associated with a rise in arterial EPO and free radical-mediated reduction in nitric oxide, indicative of oxidative-nitrosative stress. The latter was confirmed by an increased systemic formation of A˙(-) , PBN-OR, 3-NT and corresponding loss of NO2- (P < 0.05 vs. normoxia). The erythropoietic and oxidative-nitrosative stress responses were consistently related (r = -0.52 to 0.68, P < 0.05).

CONCLUSION

These findings demonstrate that EPO has the capacity to act as a biological antioxidant and provide a mechanistic basis for its reported cytoprotective benefits within the clinical setting.

Disordered vascular compliance in haemochromatosis

BACKGROUND

A relationship may exist between body iron stores, endothelial dysfunction and overall cardiovascular risk.

AIMS

To compare vascular compliance, biochemical endothelial function and antioxidant status between patients with homozygous hereditary haemochromatosis and healthy controls.

METHODS

Haemochromatosis patients and healthy controls were recruited. Measures of vascular compliance were assessed by applanation tonometry. Serological markers of endothelial function (plasma lipid hydroperoxides, cell adhesion molecules), antioxidant levels (ascorbate, lipid soluble antioxidants) and high-sensitivity C-reactive protein (CRP) were also measured.

RESULTS

Thirty-five hereditary haemochromatosis patients (ten females, mean age 54.6) and 36 controls (27 female, mean age 54.0) were recruited. Haemochromatosis patients had significantly higher systolic and diastolic blood pressures. Pulse wave velocity (PWV) was significantly higher in male haemochromatosis patients (9.90 vs. 8.65 m/s, p = 0.048). Following adjustment for age and blood pressure, male haemochromatosis patients continued to have a trend for higher PWVs (+1.37 m/s, p = 0.058). Haemochromatosis patients had significantly lower levels of ascorbate (46.11 vs. 72.68 μmol/L, p = 0.011), retinol (1.17 vs. 1.81 μmol/L, p = 0.001) and g-tocopherol (2.51 vs. 3.14 μmol/L, p = 0.011). However, there was no difference in lipid hydroperoxides (0.46 vs. 0.47 nmol/L, p = 0.94), cell adhesion molecule levels (ICAM: 348.12 vs. 308.03 ng/mL, p = 0.32 and VCAM: 472.78 vs. 461.31 ng/mL, p = 0.79) or high-sensitivity CRP (225.01 vs. 207.13 mg/L, p = 0.32).

CONCLUSIONS

Haemochromatosis is associated with higher PWVs in males and diminished antioxidants across the sexes but no evidence of endothelial dysfunction or increased lipid peroxidation.

Does a diet high or low in fat influence the oxidation potential of VLDL, LDL and HDL subfractions?

BACKGROUND AND AIMS

High-fat diets have become increasingly popular for weight-loss, but their effect on the oxidation potential of lipoprotein subfractions has not been studied. Therefore, this study compared the effects of high-fat vs. low-fat weight reduction diets on this parameter.

METHODS AND RESULTS

Very-low, low- and high-density lipoprotein (VLDL, LDL & HDL) subfractions were isolated by rapid ultracentrifugation from 24-overweight/obese subjects randomised to a high- or low-fat diet. The lipoprotein subfractions were assessed for oxidation potential by measuring conjugated diene (CD) production and time at half maximum. We found a significant between-group difference in oxidation potential. Specifically, a high-fat diet led to increased CD production in VLDL(A-D) and HDL(2&3), and a prolongation of time at half maximum. Within-group differences found that CDs increased in VLDL(A&D), LDL(I-III) and HDL(2&3) in the high-fat group and fell in VLDL(A-C) and HDL(2&3) and increased in LDL(I&II), in the low-fat group. Furthermore, following both diets all lipoprotein subfractions, except LDL(II) in the low-fat group, were protected against oxidation.

CONCLUSION

These results demonstrate that at first glance, a high-fat diet may be indicative of having heart-protective properties. However, this may be erroneous, as although the time for oxidation to occur was prolonged, once this occurred these lipoproteins had the potential to produce significantly more oxidised substrate. Conversely, a low-fat diet may be considered anti-atherogenic, as these subfractions were protected against oxidation and mainly contained fewer oxidised substrate. Thus, increased fat intake may, by increasing the oxidation product within lipoprotein subfractions, increase cardiovascular disease.

Adiponectin multimers, body weight and markers of cardiovascular risk in adolescence: Northern Ireland Young Hearts Project

BACKGROUND

Research examining the relationship between adiponectin (AN) isoforms, body weight and cardiovascular (CV) risk factors is limited, particularly in younger populations.

OBJECTIVES

To investigate the inter-relationships between AN isoforms and CV risk factors, and their dependence on body weight status, in adolescents.

DESIGN

Blood samples from 92 obese, 92 overweight and 92 normal weight age- and sex-matched adolescents were analysed for traditional cardiovascular disease (CVD) risk biomarkers and also total, high molecular weight (HMW), medium and low molecular weight (LMW) AN.

RESULTS

A significant inverse association was observed between total and HMW AN and waist-hip ratio (P=0.015, P=0.006, respectively), triglycerides (P=0.003, P=0.003, respectively) and systolic blood pressure (P=0.012, P=0.024, respectively) and a significant positive association with high-density lipoprotein (P<0.001, P<0.001, respectively) in multi-adjusted analyses. There was no evidence of a relationship between multimeric AN and high-sensitivity C-reactive protein. There was also little evidence of a relationship between LMW AN and CVD risk factors. There was a strong, body mass index (BMI)-independent, association between AN, CVD biomarkers and the hypertriglyceridemic waist phenotype.

CONCLUSION

Prominent, BMI-independent associations between total and HMW AN, but not LMW AN, and CVD risk factors were already evident in this young population. This research in adolescents supports the contention that AN subfractions may have different biological actions. These associations in apparently healthy adolescents suggest an important role for AN and its subfractions in the pathogenesis of metabolic syndrome traits and indicate that the potential for total or HMW AN to act as early universal biomarkers of CV risk warrants further study.

High-altitude pulmonary hypertension is associated with a free radical-mediated reduction in pulmonary nitric oxide bioavailability

High altitude (HA)-induced pulmonary hypertension may be due to a free radical-mediated reduction in pulmonary nitric oxide (NO) bioavailability. We hypothesised that the increase in pulmonary artery systolic pressure (PASP) at HA would be associated with a net transpulmonary output of free radicals and corresponding loss of bioactive NO metabolites. Twenty-six mountaineers provided central venous and radial arterial samples at low altitude (LA) and following active ascent to 4559 m (HA). PASP was determined by Doppler echocardiography, pulmonary blood flow by inert gas re-breathing, and vasoactive exchange via the Fick principle. Acute mountain sickness (AMS) and high-altitude pulmonary oedema (HAPE) were diagnosed using clinical questionnaires and chest radiography. Electron paramagnetic resonance spectroscopy, ozone-based chemiluminescence and ELISA were employed for plasma detection of the ascorbate free radical (A(·-)), NO metabolites and 3-nitrotyrosine (3-NT). Fourteen subjects were diagnosed with AMS and three of four HAPE-susceptible subjects developed HAPE. Ascent decreased the arterio-central venous concentration difference (a-cv(D)) resulting in a net transpulmonary loss of ascorbate, α-tocopherol and bioactive NO metabolites (P < 0.05 vs. LA). This was accompanied by an increased a-cv(D) and net output of A(·-) and lipid hydroperoxides (P < 0.05 vs. sea level, SL) that correlated against the rise in PASP (r = 0.56-0.62, P < 0.05) and arterial 3-NT (r = 0.48-0.63, P < 0.05) that was more pronounced in HAPE. These findings suggest that increased PASP and vascular resistance observed at HA are associated with a free radical-mediated reduction in pulmonary NO bioavailability.

The effects of cilostazol on exercise-induced ischaemia-reperfusion injury in patients with peripheral arterial disease

OBJECTIVES

Cilostazol improves walking distance in peripheral arterial disease (PAD) patients. The study objectives were to assess the effects of cilostazol on walking distance, followed by the additional assessment of cilostazol on exercise-induced ischaemia-reperfusion injury in such patients.

METHODS

PAD patients were prospectively recruited to a double-blinded, placebo-controlled trial. Patients were randomised to receive either cilostazol 100mg or placebo twice a day. The primary end-point was an improvement in walking distance. Secondary end-points included the assessment of oxygen-derived free-radical generation, antioxidant consumption and other markers of the inflammatory cascade. Initial and absolute claudication distances (ICDs and ACDs, respectively) were measured on a treadmill. Inflammatory response was assessed before and 30 min post-exercise by measuring lipid hydroperoxide, ascorbate, alpha-tocopherol, beta-carotene, P-selectin, intracellular and vascular cell-adhesion molecules (I-CAM and V-CAM), thromboxane B(2) (TXB(2)), interleukin-6, interleukin-10, high-sensitive C-reactive protein (hsCRP), albumin-creatinine ratio (ACR) and urinary levels of p75TNF receptor. All tests were performed at baseline and 6 and 24 weeks.

RESULTS

One hundred and six PAD patients (of whom 73 were males) were recruited and successfully randomised from December 2004 to January 2006. Patients who received cilostazol demonstrated a more significant improvement in the mean percentage change from baseline in ACD (77.2% vs. 26.6% at 6 weeks, p=0.026 and 161.7% vs. 79.0% at 24 weeks, p=0.048) as compared to the placebo. Cilostazol reduced lipid hydroperoxide levels compared to a placebo-related increase before and after exercise (6 weeks: pre-exercise: -11.8% vs. +5.8%, p=0.003 and post-exercise: -12.3% vs. +13.9%, p=0.007 and 24 weeks: pre-exercise -15.5% vs. +12.0%, p=0.025 and post-exercise: -9.2% vs. +1.9%, p=0.028). beta-Carotene levels were significantly increased in the cilostazol group, compared to placebo, before exercise at 6 and 24 weeks (6 weeks: 34.5% vs. -7.4%, p=0.028; 24 weeks: 34.3% vs. 17.7%, p=0.048). Cilostazol also significantly reduced P-selectin, I-CAM and V-CAM levels at 24 weeks as compared to baseline (p<0.05). There was no difference between treatment groups for ascorbate, alpha-tocopherol, interleukin-6 and -10, hsCRP and p75TNF receptor levels.

CONCLUSIONS

Cilostazol significantly improves ACD, in addition to attenuating exercise-induced ischaemia-reperfusion injury, in PAD patients.

Molecular detection of exercise-induced free radicals following ascorbate prophylaxis in type 1 diabetes mellitus: a randomised controlled trial

AIMS/HYPOTHESIS

Patients with type 1 diabetes mellitus are more susceptible than healthy individuals to exercise-induced oxidative stress and vascular endothelial dysfunction, which has important implications for the progression of disease. Thus, in the present study, we designed a randomised double-blind, placebo-controlled trial to test the original hypothesis that oral prophylaxis with vitamin C attenuates rest and exercise-induced free radical-mediated lipid peroxidation in type 1 diabetes mellitus.

METHODS

All data were collected from hospitalised diabetic patients. The electron paramagnetic resonance spectroscopic detection of spin-trapped alpha-phenyl-tert-butylnitrone (PBN) adducts was combined with the use of supporting markers of lipid peroxidation and non-enzymatic antioxidants to assess exercise-induced oxidative stress in male patients with type 1 diabetes (HbA(1c) 7.9 +/- 1%, n = 12) and healthy controls (HbA(1c) 4.6 +/- 0.5%, n = 14). Following participant randomisation using numbers in a sealed envelope, venous blood samples were obtained at rest, after a maximal exercise challenge and before and 2 h after oral ingestion of 1 g ascorbate or placebo. Participants and lead investigators were blinded to the administration of either placebo or ascorbate treatments. Primary outcome was the difference in changes in free radicals following ascorbate ingestion.

RESULTS

Six diabetic patients and seven healthy control participants were randomised to each of the placebo and ascorbate groups. Diabetic patients (n = 12) exhibited an elevated concentration of PBN adducts (p < 0.05 vs healthy, n = 14), which were confirmed as secondary, lipid-derived oxygen-centred alkoxyl (RO.) radicals (a(nitrogen) = 1.37 mT and abeta(hydrogen) = 0.18 mT). Lipid hydroperoxides were also selectively elevated and associated with a depression of retinol and lycopene (p < 0.05 vs healthy). Vitamin C supplementation increased plasma vitamin C concentration to a similar degree in both groups (p < 0.05 vs pre-supplementation) and attenuated the exercise-induced oxidative stress response (p < 0.05 vs healthy). There were no selective treatment differences between groups in the primary outcome variable.

CONCLUSIONS/INTERPRETATION

These findings are the first to suggest that oral vitamin C supplementation provides an effective prophylaxis against exercise-induced free radical-mediated lipid peroxidation in human diabetic blood.

CLINICAL TRIALS REGISTRATION NUMBER

ISRCTN96164937.

Altered free radical metabolism in acute mountain sickness: implications for dynamic cerebral autoregulation and blood-brain barrier function

We tested the hypothesis that dynamic cerebral autoregulation (CA) and blood-brain barrier (BBB) function would be compromised in acute mountain sickness (AMS) subsequent to a hypoxia-mediated alteration in systemic free radical metabolism. Eighteen male lowlanders were examined in normoxia (21% O(2)) and following 6 h passive exposure to hypoxia (12% O(2)). Blood flow velocity in the middle cerebral artery (MCAv) and mean arterial blood pressure (MAP) were measured for determination of CA following calculation of transfer function analysis and rate of regulation (RoR). Nine subjects developed clinical AMS (AMS+) and were more hypoxaemic relative to subjects without AMS (AMS-). A more marked increase in the venous concentration of the ascorbate radical (A(*-)), lipid hydroperoxides (LOOH) and increased susceptibility of low-density lipoprotein (LDL) to oxidation was observed during hypoxia in AMS+ (P < 0.05 versus AMS-). Despite a general decline in total nitric oxide (NO) in hypoxia (P < 0.05 versus normoxia), the normoxic baseline plasma and red blood cell (RBC) NO metabolite pool was lower in AMS+ with normalization observed during hypoxia (P < 0.05 versus AMS-). CA was selectively impaired in AMS+ as indicated both by an increase in the low-frequency (0.07-0.20 Hz) transfer function gain and decrease in RoR (P < 0.05 versus AMS-). However, there was no evidence for cerebral hyper-perfusion, BBB disruption or neuronal-parenchymal damage as indicated by a lack of change in MCAv, S100beta and neuron-specific enolase. In conclusion, these findings suggest that AMS is associated with altered redox homeostasis and disordered CA independent of barrier disruption.

LDL Particle Size in Habitual Exercisers, Lean Sedentary Men and Abdominally Obese Sedentary Men

Habitual exercisers enjoy considerable protection from coronary heart disease (CHD). Often, however, only modest differences in traditional CHD risk factors are apparent between habitual exercisers and their sedentary counterparts. For this reason, there is increasing interest in novel predictors of CHD, such as a preponderance of small, dense low-density lipoprotein (LDL) particles. Polyacrylamide gel electrophoresis was used to separate lipoprotein subfractions in 32 lean exercisers, 36 lean sedentary men and 21 obese sedentary men aged 30 - 45 years. Well-validated equations were used to determine LDL concentration and peak particle diameter. Waist girth was used to identify lean (< 100 cm) and obese (>or= 100 cm) individuals. LDL concentration was lower in lean exercisers than in lean sedentary men (2.64 +/- 0.44 vs. 3.76 +/- 0.79 mmol . l (-1), p < 0.001), suggesting that habitual exercise influences this risk factor. In contrast, there were no significant differences in LDL peak particle diameter between lean exercisers, lean sedentary men and obese sedentary men (27.92 +/- 0.67, 28.09 +/- 0.62 and 27.77 +/- 0.77 nm, respectively). In multiple linear regression analysis, triglyceride concentration was the only significant predictor of LDL PPD. These data suggest that habitual exercise influences LDL concentration but does not influence LDL particle size in men aged 30 - 45 years.

Oxidative modification of triacylglycerol-rich lipoproteins

Lipoprotein oxidation is thought to play a pivotal role in the evolution of atherosclerosis. Low-density lipoprotein (LDL) is the main source of oxidized lipid in the arterial wall. Oxidation of LDL alters its properties in a number of ways, making it more atherogenic, but oxidation of other lipoprotein classes may also be important. Common mechanisms are likely to contribute to the oxidation of all lipoprotein classes, with enzyme-mediated oxidation likely to be most important. Antioxidant content, fatty acid composition, particle size and the presence of seeding hydroperoxides also influence oxidative reactions. Larger triglyceride-rich lipoproteins are less likely to enter the arterial wall than LDL, but when oxidized will deliver a greater oxidant load to the arterial wall.

Effects of GH on lipid peroxidation and neutrophil superoxide anion-generating capacity in hypopituitary adults with GH deficiency

OBJECTIVES

Untreated growth hormone deficiency (GHD) is implicated in the increased cardiovascular risk associated with adult hypopituitarism. Oxidative stress, predisposing to lipid peroxidation, may be an important mediator of endothelial dysfunction, a pro-atherogenic state associated with adult GHD.

DESIGN AND PATIENTS

In a randomized, double-blind, placebo-controlled study we investigated the effects of GH replacement on low-density lipoprotein (LDL) oxidation and neutrophil superoxide (O(-)(2)) generating capacity in 32 GHD adults (19 males, 13 females; age range 19-64 years) over 3 months. Thirty age- and sex-matched healthy controls were also studied.

MEASUREMENTS

Lipid hydroperoxides (HPOs) in plasma were measured using the ferrous oxidation with xylenol orange (FOX) assay. The susceptibility of LDL to oxidation was assessed by the copper-catalysed lag phase of LDL oxidation. Neutrophil O(-)(2)- generating capacity was assessed by a lucigenin-based chemiluminescent assay of NADPH oxidase activity. Body composition was assessed using bioelectrical impedance analysis.

RESULTS

Compared to controls, GHD subjects had higher LDL cholesterol (4.0 +/- 0.8 vs. 3.5 +/- 0.9 mmol/l, P < 0.01) and higher triglyceride concentrations (2.3 +/- 1.5 vs. 1.1 +/- 0.7 mmol/l, P < 0.001) but lower HDL cholesterol (1.1 +/- 0.3 mmol/l vs. 1.4 +/- 0.4 mmol/l, P < 0.01), lower levels of HPOs (0.72 +/- 0.35 vs. 0.92 +/- 0.20 microm, P < 0.01) and lower basal (2.5 +/- 1.5 vs. 4.5 +/- 2.3 mV/5 x 10(5) neutrophils, P < 0.01) and peak post-activation levels (23.2 +/- 11.1 vs. 34.4 +/- 15.6 mV/5 x 10(5) neutrophils, P < 0.01) of neutrophil O(-)(2)- generation. GH replacement resulted in an increase in HPOs from 0.70 +/- 0.39 to 0.86 +/- 0.19 microm (P < 0.05), although there was no change in the lag time of LDL oxidation. Neutrophil O(-)(2)- generating capacity was enhanced with a rise in basal O(-)(2)- generation from 2.8 +/- 1.4 to 5.4 +/- 4.6 mV/5 x 10(5) neutrophils (P < 0.05) and in peak post-activation O(-)(2)- generation from 21.9 +/- 9.5 to 35.8 +/- 21.7 mV/5 x 10(5) neutrophils (P < 0.05). LDL cholesterol was reduced from 4.1 +/- 0.8 mmol/l to 3.5 +/- 0.8 mmol/l (P < 0.01). No significant changes in measured parameters occurred in the placebo group.

CONCLUSIONS

Adult GHD is associated with reduced lipid peroxidation and impaired neutrophil O(-)(2)- generating capacity, both of which are reversible with GH replacement. Our data suggest that: (i) that oxidative stress is not a major feature of the pro-atherogenic state in hypopituitary adults with GHD and (ii) a role for GH in modulating neutrophil function and leucocyte-lipoprotein interactions.

Lipoprotein oxidation and atherosclerosis

Lipoprotein oxidation is a key early stage in the development of atherosclerosis. Oxidation of low-density lipoprotein (LDL) is initiated by both enzyme-mediated and non-enzymic mechanisms in vivo, and oxidized LDL has many atherogenic properties. Oxidation of LDL in vivo is likely to be influenced by local environmental factors, such as pH. The composition of LDL is also important, including such factors as antioxidant content, fatty acid composition and particle size.

Reperfusion injury is greater with delayed restoration of venous outflow in concurrent arterial and venous limb injury

BACKGROUND

Complex limb trauma often involves combined arterial and venous injury, and the resultant ischaemia-reperfusion injury (IRI) causes both local and remote organ injury. This study assessed the influence of the timing of restoration of venous drainage on IRI.

METHODS

Male New Zealand white rabbits (n = 36) were randomized into six groups: sham operation (group 1) and unilateral hind limb arterial and venous occlusion for 1 h followed by no reflow for 2 h (group 2), arterial and venous reflow for 2 h (group 3), arterial reflow alone for 2 h (group 4), arterial reflow alone for 1 h followed by arterial and venous (delayed) reflow for a further 1 h (group 5), and pretreatment with an enteral combination antioxidant before occlusion of both artery and vein and delayed venous reflow (group 6). Plasma hydroperoxide (HPO) and glutathione peroxidase concentration, hind limb skeletal muscle and lung tissue wet : dry weight ratios and myeloperoxidase (MPO) concentration were measured.

RESULTS

The plasma HPO level in the femoral vein effluent was significantly greater after delayed venous reflow (mean(s.e.m.) 2. 02(0.54) micromol/l) than in control animals (0.98(0.10) micromol/l) (P < 0.05). There was also a significantly greater tissue wet : dry weight ratio after delayed venous reflow than in controls, in skeletal muscle (mean(s.e.m.) 6.89(0.14) versus 5.34(0.54); P < 0. 05) and lung (9.20(1.14) versus 7.23(0.38); P < 0.05) tissue. Lung tissue MPO activity was significantly greater after delayed venous reflow compared with controls (3.20(0.28) versus 1.86(0.14) units/g; P < 0.005), and also in comparison to simultaneous arterial and venous reflow (2.40(0.24) units/g; P < 0.05). In the antioxidant pretreatment group there was no significant increase in plasma HPO concentration, tissue MPO level or tissue wet : dry weight ratio compared with the control group.

CONCLUSION

In combined major arterial and venous injury of the limb, delayed restoration of venous drainage leads to significantly greater local skeletal muscle injury and remote neutrophil-mediated lung injury. These results support the clinical rationale for early restoration not only of arterial inflow but also venous drainage by means of intraluminal shunts.

Very low density lipoprotein subfractions in Type II diabetes mellitus: alterations in composition and susceptibility to oxidation

AIMS/HYPOTHESIS

Type II (non-insulin-dependent) diabetes mellitus is associated with raised triglycerides and increased very low density lipoprotein cholesterol. The aim of this study was to assess if very low density lipoprotein subfraction composition and potential to oxidise were altered in this condition.

METHODS

Very low density lipoprotein was separated into four subfractions (A-->D) by a novel, rapid ultracentrifugation procedure. Analysis of each subfraction included lipid and fatty acid composition. Preformed peroxides were measured spectrophotometrically and conjugated dienes were used as an indicator of in vitro lipid oxidation.

RESULTS

In all results we compared patient and control subfractions. Mean fasting plasma glucose was 8.9 +/- 2.0 mmol/l in patients vs 5.1 +/- 0.4 mmol/l in control subjects (p < 0.001); patient HbA1c was 7.6 +/- 1.4%. Patient total lipid standardised for apo B was higher than controls in subfractions A, B and C; A, 201 vs 60; B, 191 vs 40; C, 63 vs 21; D, 29 vs 34 micromol lipid per mg apo B (p < 0.05). Preformed peroxides were higher in all patient subfractions compared with controls: A, 340 vs 48; B, 346 vs 42; C, 262 vs 28; D, 54 vs 16 nmol per mg apo B (p < 0.001). Patient subfractions A and D were more susceptible to in vitro oxidation. Monounsaturated fatty acids were lower in patients subfractions, 35.2 vs 36.7; B, 35.1 vs 38.7; C, 34.4 vs 36.5; D, 33.0 vs 35.5 as per cent total (p < 0.05).

CONCLUSIONS/INTERPRETATION

These results indicate abnormalities in very low density lipoprotein subfraction composition and oxidation profile in Type II diabetic subjects, which are characteristic of more atherogenic particles and that may contribute to the development of cardiovascular disease in these patients.

HDL composition and HDL antioxidant capacity in patients on regular haemodialysis

Recent evidence suggests that HDL can directly inhibit LDL oxidation, a key early stage in atherogenesis. Patients with chronic renal failure are at increased cardiovascular risk, have reduced HDL levels and altered HDL composition. We have therefore investigated whether compositional changes in HDL lead to decreased HDL antioxidant capacity in these patients. In comparison to control subject HDL, patient HDL contained less total cholesterol, cholesterol esters, phospholipids and alpha-tocopherol. LDL, HDL and LDL + HDL were standardised for protein and oxidised in the presence of Cu2+. The rate of propagation during HDL oxidation was reduced in the patient group (3.28+/-0.65 x 10(-5) vs. 4.60+/-0.97 x 10(-5) abs. U/min, P < 0.01). Lipid peroxide generation in patient HDL was decreased: 6.56+4.4 versus 13.42+/-7.0 nmol malondialdehyde (MDA)/mg HDL protein after 90 min and 14.45+/-3.8 versus 20.11+/-7.8 nmol MDA/mg HDL protein after 180 min. This is attributable to reduced HDL polyunsaturated fatty acid content in patients (0.53+/-0.12 vs. 0.72+/-0.16 mmol/g HDL, P < 0.01). The inhibitory effect of HDL on LDL oxidation was similar: 71 and 33% for patient HDL compared to 68 and 31% for control HDL, after 90 and 180 min, respectively. Compositional changes of HDL in patients on haemodialysis did not affect the antioxidant capacity of HDL after standardisation for HDL protein. However, reduced HDL levels in vivo may result in reduced HDL antioxidant capacity in these patients.

Absorption and antioxidant effects of quercetin from onions, in man

OBJECTIVE

To investigate the in vivo effects of quercetin following the ingestion of fried onions.

DESIGN

Five healthy volunteers, three males and two females aged between 25 and 39 y, ingested 225 g of fried onions after an overnight fast and peripheral venous blood was collected 0, 2, 4, 24 and 48 h after consumption. Quercetin in the plasma, total antioxidant capacity and susceptibility of low density lipoproteins (LDL) to oxidation were measured.

RESULTS

Following the onion meal, quercetin levels increased from baseline values (28.4 +/- 1.9 ng/ml) to peak after 2 h (248.4 +/- 103.9 ng/ml), decreasing to baseline again after 24 h (P > 0.05). This was accompanied by an increase in the total antioxidant activity of the plasma from baseline (1.70 +/- 0.04 mmol/l trolox equivalents) to 1.75 +/- 0.10 mmol/l trolox equivalents after 2 h and 1.76 +/- 0.08 mmol/l trolox equivalents after 4 h. There was no significant change in the susceptibility of the plasma or the isolated LDL to oxidation over the 48 h period after consumption of the fried onions. In view of these negative findings, we isolated LDL and other lipoproteins from plasma at each time point. Quercetin was not detected in either LDL or VLDL, but was present in the HDL fraction, although this fraction also contains other proteins including albumin.

CONCLUSIONS

Quercetin can be absorbed in humans from dietary sources to high enough concentrations to increase the overall antioxidant activity of the plasma. Quercetin, however, has a strong affinity for protein and provides no direct protective effect during LDL oxidation.

A simple method for assessing copper-mediated oxidation of very-low-density lipoprotein isolated by rapid ultracentrifugation

The association of very-low-density lipoprotein (VLDL) with atherosclerosis remains controversial. However, studies have shown that oxidative modification of VLDL can promote foam cell formation, leading to the development of atherosclerosis. A rapid method is described which will allow the significance of VLDL oxidation to be assessed in clinical studies. VLDL was isolated from heparinized plasma by a 1-h, single spin ultracentrifugation. Total protein was standardized to 25 mg/L. Oxidation was promoted by the addition of copper ions (17.5 mumol/L, final concentration) incubated at 37 degrees C. Conjugated diene production was followed at 234 nm. Total assay preparation time was 2 h. Urate greatly inhibited the oxidation of VLDL and was successfully removed by size exclusion chromatography. VLDL isolated from frozen plasma (-70 degrees C) was stable for 15 weeks. This simple, rapid method for the isolation of VLDL may be applied to assess the significance of VLDL oxidation in disease.

Black tea consumption does not protect low density lipoprotein from oxidative modification

OBJECTIVE

To investigate the in vivo and in vitro effects of black tea on the oxidative modification of low density lipoprotein (LDL).

DESIGN

The antioxidant activity of the tea was studied in vitro by measuring the resistance of the LDL to oxidative modification in the presence of copper. The effects of tea consumption in vivo were investigated in two settings. Firstly, to assess the acute effects of tea consumption, five fasting healthy subjects ingested 600 mls (50.7+/-5.4 mg flavonoids) of black tea and peripheral venous blood was collected at 0, 30, 60, 90, 120 and 180 min after consumption. Secondly, to assess the effects of chronic tea consumption, a randomised crossover trial of tea (126.8+/-13.5 mg flavonoids) and coffee consumption was carried out in ten healthy subjects.

RESULTS

Black tea extract increased the resistance of LDL in vitro in a concentration dependent manner. There was no significant change in total plasma antioxidant capacity or susceptibility of the LDL to oxidation over the 3 h period after consumption of black tea. The four-week crossover study in which coffee was used as a control against the black tea showed no significant difference in the total plasma antioxidant capacity or susceptibility of LDL to oxidation between the tea and coffee groups. Serum lipids, including total cholesterol, triglycerides, LDL cholesterol and HDL cholesterol did not change significantly throughout the study.

CONCLUSIONS

The consumption of moderate quantities of black tea acutely or for one week does not increase plasma total antioxidant capacity or alter the susceptibility of LDL to oxidation.

Susceptibility of VLDL to oxidation in patients on regular haemodialysis

Oxidation of VLDL in vitro increases macrophage uptake and promotes foam cell formation, and the dyslipidaemia of chronic renal failure is characterised by an increase in VLDL. However, little information is available with regard to the susceptibility of VLDL to oxidation in patients at increased risk of atherosclerosis. We have therefore assessed the composition and susceptibility to oxidation of VLDL from haemodialysis patients and control subjects. VLDL from haemodialysis patients contained increased lipid hydroperoxides (81.6 +/- 12.6 versus 16.1 +/- 3.4 nmol/mg protein, P < 0.001) and malondialdehyde (35.9 +/- 7.3 versus 16.0 +/- 4.1 nmol/mg protein, P < 0.05). Susceptibility to oxidation was increased as shown by an increased rate of propagation of the copper induced lipid peroxidation chain-reaction (11.6 +/- 1.5 x 10(-5) versus 7.6 +/- 1.1 x 10(-5)abs. U/min, P < 0.05) and a greater increase in conjugated diene formation during peroxidation (0.47 +/- 0.04 versus 0.25 +/- 0.03 abs. U, P < 0.001). Increased VLDL peroxidation in dialysis patients may contribute to the increased risk of cardiovascular disease observed in this group of patients.

The effect of various oestrogens and progestogens on the susceptibility of low density lipoproteins to oxidation in vitro

OBJECTIVE

To investigate the effect of different oestrogens and progestogens, at various concentrations, on the oxidation of low density lipoproteins (LDL) in vitro.

METHODS

Oestradiol, oestrone, oestriol and equilin, as well as medroxyprogesterone acetate, norgestrel and norethisterone, were added to isolated male LDL, before it was oxidised in the presence of copper ions at 37 degrees C. The oxidation process was monitored spectrophotometrically by the production of conjugated dienes. The lag time to oxidation and the maximum rate of propagation of the reaction were used as measures of the resistance and susceptibility of the LDL to oxidation respectively.

RESULTS

The lag time was increased from 43.7 +/- 1.5 min (mean +/- SEM) for LDL without any added hormone, to 81.2 +/- 1.0 min by 1 microM oestradiol (P < 0.01), 77.9 +/- 4.6 min by 1 microM oestrone (P < 0.01), 67.6 +/- 6.2 min by 1 microM equilin (P < 0.01), and 51.8 +/- 2.8 min by 1 microM oestriol (P < 0.05). The maximum rate of propagation of the reaction was decreased from 0.23 +/- 0.01 nmol conjugated dienes/mg LDL-protein/min (mean +/- SEM) (control LDL) to 0.14 +/- 0.006 nmol/mg/min by oestradiol (P < 0.01), 0.15 +/- 0.009nmol/mg/min by oestrone (P < 0.01), 0.17 +/- 0.012 nmol/mg/min by equilin (P < 0.01) and 0.19 +/- 0.014 nmol/mg/min (P < 0.05) by oestriol. The progestogens alone had no antioxidant effect, nor did their addition to the oestrogens influence their antioxidant activity.

CONCLUSIONS

These results demonstrate that all oestrogens investigated have an inhibitory effect on LDL oxidation in vitro. The magnitude of this effect varied, being of the order oestradiol > oestrone > equilin > oestriol.

Carbamylation inhibits the ferroxidase activity of caeruloplasmin

The ferroxidase activity of caeruloplasmin (EC 1.16.3.1) is an important antioxidant defence mechanism in man. In chronic renal failure proteins become carbamylated as a result of reactions with urea-derived cyanate. We have therefore investigated the effects of carbamylation on the ferroxidase activity of caeruloplasmin. Increasing degrees of carbamylation produce a progressive impairment of ferroxidase activity measured using o-dianisidine as substrate, and the ability of caeruloplasmin to load ferrous iron onto ovotransferrin is reduced. Carbamylation of caeruloplasmin may contribute to reduced antioxidant capacity in patients with renal failure.

A rapid method for measurement of the susceptibility to oxidation of low-density lipoprotein

Oxidation of low-density lipoprotein (LDL) may be important in the pathogenesis of atherosclerosis. We describe a method which measures the oxidation resistance of LDL isolated by a rapid procedure without added antioxidants. LDL was isolated from heparinized plasma by density gradient ultracentrifugation and desalted by gel filtration. The protein concentration was standardized to 50 mg/L and oxidation was promoted by copper (2 mumol/L) at 37 degrees C. The total sample preparation time was 2.5 h. Conjugated diene production was monitored at lambda = 234 nm with computation of the lag time. LDL oxidation was inhibited by EDTA but not heparin. Albumin inhibited LDL oxidation but only in concentrations greater than 50 mg/L. LDL was stable in frozen plasma (-70 degrees C) for 10 weeks, but unstable in the isolated and desalted state. The lag time for LDL from patients treated with the antioxidant probucol was markedly prolonged compared to normal subjects.

The effect of probucol and vitamin E treatment on the oxidation of low-density lipoprotein and forearm vascular responses in humans

This study investigates the hypothesis that lipid soluble antioxidants may increase the resistance of low-density lipoprotein (LDL) to oxidation and also enhance vascular endothelial responses in humans. In a double-blind parallel group study, 24 hypercholesterolaemic patients already on treatment with simvastatin (20 mg day-1), were randomized to supplementary treatment with probucol (500 mg bd), vitamin E (400 IU daily) or placebo for 8 weeks. Mean serum cholesterol before antioxidant treatment was 7.00 mmol l-1. Resistance of LDL to oxidation by copper was increased by 830% in the probucol group and by 30% in the vitamin E group. However, thiobarbituric acid reacting substances in whole serum were not altered by either antioxidant. Probucol lowered HDL- and LDL-cholesterol levels and increased the QT interval. Forearm vascular responses, as measured by venous occlusion plethysmography, to acetylcholine, glyceryl trinitrate and NG-monomethyl-L-arginine, were not significantly changed by antioxidant treatment. Probucol has a major, and vitamin E a minor, effect on LDL resistance to oxidation but neither compound appears to alter forearm vascular responses in vivo.

Oxidation of low density lipoprotein in patients on regular haemodialysis

Patients undergoing chronic haemodialysis are known to have a high incidence of premature atherosclerosis for reasons which have not been fully elucidated. The susceptibility of low density lipoprotein (LDL) to oxidation by copper ions in vitro is widely used as a measure of its atherogenicity in vivo. We measured the susceptibility of LDL to oxidation using copper ions in haemodialysis patients and found, surprisingly, a markedly increased resistance to oxidation. The experiment was therefore repeated using an alternative free radical generator, AAPH [2,2'-azobis-(2-amidinopropane hydrochloride)], to promote LDL oxidation; using AAPH, the susceptibility to oxidation was similar in the dialysis group compared to controls. Abnormal LDL composition in the dialysis patients was also demonstrated. We suggest that, in such situations, susceptibility of LDL to oxidation in vitro may be highly dependent on the biochemical method employed and therefore may not accurately reflect atherogenic risk.

Rare apolipoprotein E variant identified in a patient with type III hyperlipidaemia

We report a rare apolipoprotein E variant in an Irish female with Type III hyperlipidaemia who has the phenotype E2E1 as determined by isoelectric focusing. Sequence analysis of the apolipoprotein E gene from the proband and from four other family members, using DNA amplified by the polymerase chain reaction, demonstrated the presence of a point mutation in the common epsilon 2 allele with a G-->A transition at nucleotide 3791. This was confirmed by digestion with the restriction endonuclease TaqI, which cuts at a new site within the apolipoprotein E gene, created by the base change. This mutation results in a substitution of aspartic acid for glycine at position 127 of the mature protein. We believe this to be the first description of this apolipoprotein E variant in a family from the British Isles. The mutation appears to be 'recessive' with respect to the expression of Type III hyperlipidaemia, although it may be somewhat more potent in this regard than the parent epsilon 2 allele. The Type III hyperlipidaemia is responsive to treatment with diet and gemfibrozil.

Pre-beta high-density lipoprotein determined by immunoblotting with chemiluminescent detection

We describe a novel assay of pre-beta high-density lipoprotein (HDL), a unique apolipoprotein A-I (apo A-I)-containing lipoprotein particle. The pre-beta and alpha lipoproteins are separated by electrophoresis in agarose and transferred onto a membrane by capillary blotting. The membrane blot is sequentially incubated with sheep anti-human apo A-I antiserum and then with a conjugate of rabbit anti-sheep immunoglobulin and horseradish peroxidase. Chemiluminescence formed by the peroxidase-catalyzed oxidation of luminol in the presence of an enhancer is captured on photographic film, and the pre-beta HDL band is quantified by transmission densitometry. The assay is calibrated with standards prepared from a reference serum diluted in 9 mol/L urea. Within-batch precision (CV) at pre-beta HDL concentrations of 22.1 and 44.3 mg/L was 7% and 4.9% respectively. Pre-beta HDL contained 1.6% (0.65-2.6%, mean and range) of total serum apo A-I in 30 normolipidemic subjects.

Pre-Beta High-Density Lipoprotein Determined by Immunoblotting with Chemiluminescent Detection

We describe a novel assay of pre-beta high-density lipoprotein (HDL), a unique apolipoprotein A-I (apo A-I)-containing lipoprotein particle. The pre-beta and alpha lipoproteins are separated by electrophoresis in agarose and transferred onto a membrane by capillary blotting. The membrane blot is sequentially incubated with sheep anti-human apo A-I antiserum and then with a conjugate of rabbit anti-sheep immunoglobulin and horseradish peroxidase. Chemiluminescence formed by the peroxidase-catalyzed oxidation of luminol in the presence of an enhancer is captured on photographic film, and the pre-beta HDL band is quantified by transmission densitometry. The assay is calibrated with standards prepared from a reference serum diluted in 9 mol/L urea. Within-batch precision (CV) at pre-beta HDL concentrations of 22.1 and 44.3 mg/L was 7% and 4.9% respectively. Pre-beta HDL contained 1.6% (0.65-2.6%, mean and range) of total serum apo A-I in 30 normolipidemic subjects.